Bump mpdf/mpdf from 6.1.4 to 7.1.8

Bumps [mpdf/mpdf](https://github.com/mpdf/mpdf) from 6.1.4 to 7.1.8.
- [Release notes](https://github.com/mpdf/mpdf/releases)
- [Changelog](https://github.com/mpdf/mpdf/blob/development/CHANGELOG.md)
- [Commits](https://github.com/mpdf/mpdf/compare/v6.1.4...v7.1.8)

Signed-off-by: dependabot[bot] <support@dependabot.com>

composer.json

@@ -2,7 +2,7 @@
   "require" : {
     "php": "^5.6.0",
     "ext-mbstring": "*",
-    "mpdf/mpdf": "^6.1"
+    "mpdf/mpdf": "^7.1"
   },
   "require-dev": {
     "heroku/heroku-buildpack-php": "*"

composer.lock

@@ -1,61 +1,218 @@
 {
     "_readme": [
         "This file locks the dependencies of your project to a known state",
-        "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file",
+        "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "05cf563300c13b4b6b613c7b72940056",
+    "content-hash": "0a7f230938b280a92c152684f7dcea64",
     "packages": [
         {
             "name": "mpdf/mpdf",
-            "version": "v6.1.4",
+            "version": "v7.1.8",
             "source": {
                 "type": "git",
                 "url": "https://github.com/mpdf/mpdf.git",
-                "reference": "e7310ce53b5c11db1f0b781fe0a69066608ac6e2"
+                "reference": "5a124ed382cf9241597c7ba12f98a756daa7f8df"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/mpdf/mpdf/zipball/e7310ce53b5c11db1f0b781fe0a69066608ac6e2",
+                "url": "https://api.github.com/repos/mpdf/mpdf/zipball/5a124ed382cf9241597c7ba12f98a756daa7f8df",
-                "reference": "e7310ce53b5c11db1f0b781fe0a69066608ac6e2",
+                "reference": "5a124ed382cf9241597c7ba12f98a756daa7f8df",
                 "shasum": ""
             },
             "require": {
+                "ext-gd": "*",
                 "ext-mbstring": "*",
-                "php": "^5.4.0 || 7.0.*",
+                "myclabs/deep-copy": "^1.7",
+                "paragonie/random_compat": "^1.4|^2.0|9.99.99",
+                "php": "^5.6 || ~7.0.0 || ~7.1.0 || ~7.2.0 || ~7.3.0",
+                "psr/log": "^1.0",
                 "setasign/fpdi": "1.6.*"
             },
             "require-dev": {
-                "phpunit/phpunit": "^4.7"
+                "mockery/mockery": "^0.9.5",
+                "phpunit/phpunit": "^5.0",
+                "squizlabs/php_codesniffer": "^2.7.0",
+                "tracy/tracy": "^2.4"
             },
             "suggest": {
+                "ext-bcmath": "Needed for generation of some types of barcodes",
+                "ext-xml": "Needed mainly for SVG manipulation",
                 "ext-zlib": "Needed for compression of embedded resources, such as fonts"
             },
             "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-development": "7.x-dev"
+                }
+            },
             "autoload": {
-                "classmap": [
+                "psr-4": {
-                    "mpdf.php",
+                    "Mpdf\\": "src/"
-                    "classes"
+                }
-                ]
             },
             "notification-url": "https://packagist.org/downloads/",
             "license": [
-                "GPL-2.0"
+                "GPL-2.0-only"
             ],
             "authors": [
+                {
+                    "name": "Matěj Humpál",
+                    "role": "Developer, maintainer"
+                },
                 {
                     "name": "Ian Back",
-                    "role": "Developer"
+                    "role": "Developer (retired)"
                 }
             ],
-            "description": "A PHP class to generate PDF files from HTML with Unicode/UTF-8 and CJK support",
+            "description": "PHP library generating PDF files from UTF-8 encoded HTML",
-            "homepage": "http://mpdf.github.io",
+            "homepage": "https://mpdf.github.io",
             "keywords": [
                 "pdf",
                 "php",
                 "utf-8"
             ],
-            "time": "2017-07-09T16:46:12+00:00"
+            "time": "2019-01-08T11:38:17+00:00"
+        },
+        {
+            "name": "myclabs/deep-copy",
+            "version": "1.8.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/myclabs/DeepCopy.git",
+                "reference": "3e01bdad3e18354c3dce54466b7fbe33a9f9f7f8"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/myclabs/DeepCopy/zipball/3e01bdad3e18354c3dce54466b7fbe33a9f9f7f8",
+                "reference": "3e01bdad3e18354c3dce54466b7fbe33a9f9f7f8",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^7.1"
+            },
+            "replace": {
+                "myclabs/deep-copy": "self.version"
+            },
+            "require-dev": {
+                "doctrine/collections": "^1.0",
+                "doctrine/common": "^2.6",
+                "phpunit/phpunit": "^7.1"
+            },
+            "type": "library",
+            "autoload": {
+                "psr-4": {
+                    "DeepCopy\\": "src/DeepCopy/"
+                },
+                "files": [
+                    "src/DeepCopy/deep_copy.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "description": "Create deep copies (clones) of your objects",
+            "keywords": [
+                "clone",
+                "copy",
+                "duplicate",
+                "object",
+                "object graph"
+            ],
+            "time": "2018-06-11T23:09:50+00:00"
+        },
+        {
+            "name": "paragonie/random_compat",
+            "version": "v9.99.99",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/paragonie/random_compat.git",
+                "reference": "84b4dfb120c6f9b4ff7b3685f9b8f1aa365a0c95"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/paragonie/random_compat/zipball/84b4dfb120c6f9b4ff7b3685f9b8f1aa365a0c95",
+                "reference": "84b4dfb120c6f9b4ff7b3685f9b8f1aa365a0c95",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^7"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "4.*|5.*",
+                "vimeo/psalm": "^1"
+            },
+            "suggest": {
+                "ext-libsodium": "Provides a modern crypto API that can be used to generate random bytes."
+            },
+            "type": "library",
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Paragon Initiative Enterprises",
+                    "email": "security@paragonie.com",
+                    "homepage": "https://paragonie.com"
+                }
+            ],
+            "description": "PHP 5.x polyfill for random_bytes() and random_int() from PHP 7",
+            "keywords": [
+                "csprng",
+                "polyfill",
+                "pseudorandom",
+                "random"
+            ],
+            "time": "2018-07-02T15:55:56+00:00"
+        },
+        {
+            "name": "psr/log",
+            "version": "1.1.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/php-fig/log.git",
+                "reference": "6c001f1daafa3a3ac1d8ff69ee4db8e799a654dd"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/php-fig/log/zipball/6c001f1daafa3a3ac1d8ff69ee4db8e799a654dd",
+                "reference": "6c001f1daafa3a3ac1d8ff69ee4db8e799a654dd",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.3.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.0.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Psr\\Log\\": "Psr/Log/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "PHP-FIG",
+                    "homepage": "http://www.php-fig.org/"
+                }
+            ],
+            "description": "Common interface for logging libraries",
+            "homepage": "https://github.com/php-fig/log",
+            "keywords": [
+                "log",
+                "psr",
+                "psr-3"
+            ],
+            "time": "2018-11-20T15:27:04+00:00"
         },
         {
             "name": "setasign/fpdi",