Bump postcss-cli from 6.1.3 to 7.0.0

Bumps [postcss-cli](https://github.com/postcss/postcss-cli) from 6.1.3 to 7.0.0.
- [Release notes](https://github.com/postcss/postcss-cli/releases)
- [Changelog](https://github.com/postcss/postcss-cli/blob/master/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss-cli/compare/6.1.3...7.0.0)

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

package.json

@@ -50,7 +50,7 @@
     "markdownlint-cli": "~0.21.0",
     "netlify-cli": "^2.25.0",
     "npm-run-all": "^4.1.5",
-    "postcss-cli": "^6.1.3",
+    "postcss-cli": "^7.0.0",
     "rimraf": "^3.0.0",
     "stylelint": "~12.0.1",
     "stylelint-config-recommended-scss": "~4.1.0",