build(deps-dev): Bump mini-css-extract-plugin in /frontend (#346)

Bumps [mini-css-extract-plugin](https://github.com/webpack-contrib/mini-css-extract-plugin) from 0.8.2 to 0.9.0.
- [Release notes](https://github.com/webpack-contrib/mini-css-extract-plugin/releases)
- [Changelog](https://github.com/webpack-contrib/mini-css-extract-plugin/blob/master/CHANGELOG.md)
- [Commits](webpack-contrib/mini-css-extract-plugin@v0.8.2...v0.9.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

frontend/package.json

@@ -38,7 +38,7 @@
     "eslint-plugin-prettier": "^3.1.0",
     "file-loader": "^5.0.1",
     "html-webpack-plugin": "^3.2.0",
-    "mini-css-extract-plugin": "^0.8.0",
+    "mini-css-extract-plugin": "^0.9.0",
     "node-sass": "^4.12.0",
     "optimize-css-assets-webpack-plugin": "^5.0.3",
     "prettier": "1.19.1",