Chore(deps): Bump mini-css-extract-plugin from 2.8.1 to 2.9.0

Bumps [mini-css-extract-plugin](https://github.com/webpack-contrib/mini-css-extract-plugin) from 2.8.1 to 2.9.0.
- [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@v2.8.1...v2.9.0)

---
updated-dependencies:
- dependency-name: mini-css-extract-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

package.json

@@ -40,7 +40,7 @@
                 "guid-typescript": "1.0.9",
                 "isomorphic-fetch": "3.0.0",
                 "localforage": "1.10.0",
-                "mini-css-extract-plugin": "2.8.1",
+                "mini-css-extract-plugin": "2.9.0",
                 "monaco-editor": "0.30.1",
                 "monaco-editor-webpack-plugin": "6.0.0",
                 "office-ui-fabric-core": "11.1.0",