Update css-loader requirement in /{{cookiecutter.app_name}}

Updates the requirements on [css-loader](https://github.com/webpack-contrib/css-loader) to permit the latest version.
- [Release notes](https://github.com/webpack-contrib/css-loader/releases)
- [Changelog](https://github.com/webpack-contrib/css-loader/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack-contrib/css-loader/compare/v2.1.1...v3.0.0)

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

{{cookiecutter.app_name}}/package.json

@@ -35,7 +35,7 @@
     "babel-loader": "^8.0.6",
     "babel-preset-env": "^1.7.0",
     "concurrently": "^4.1.0",
-    "css-loader": "^2.1.1",
+    "css-loader": "^3.0.0",
     "eslint-config-airbnb-base": "^13.1.0",
     "eslint-plugin-import": "^2.17.3",
     "eslint": "^5.16.0",