Update dependencies and drop Node.js 8.x support

The package will still work, but Node.js 8.x is EOL since 31/12/2019.

.travis.yml

@@ -1,6 +1,5 @@
 language: node_js
 node_js:
-  - "8"
   - "10"
   - "12"
   - "14"

package.json

@@ -18,8 +18,8 @@
   },
   "devDependencies": {
     "bin-check": "^4.1.0",
-    "eslint": "^6.8.0",
-    "mocha": "^7.2.0"
+    "eslint": "^7.10.0",
+    "mocha": "^8.1.3"
   },
   "scripts": {
     "eslint": "eslint .",
@@ -33,7 +33,7 @@
     "index.js"
   ],
   "engines": {
-    "node": ">=8"
+    "node": ">=10"
   },
   "eslintConfig": {
     "extends": "eslint:recommended",