Bump mini-css-extract-plugin from 0.4.1 to 0.4.2 in /js

Bumps [mini-css-extract-plugin](https://github.com/webpack-contrib/mini-css-extract-plugin) from 0.4.1 to 0.4.2.
- [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](https://github.com/webpack-contrib/mini-css-extract-plugin/compare/v0.4.1...v0.4.2)

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

js/package.json

@@ -26,7 +26,7 @@
     "babel-preset-env": "^1.7.0",
     "css-loader": "^1.0.0",
     "karma": "^3.0.0",
-    "mini-css-extract-plugin": "^0.4.1",
+    "mini-css-extract-plugin": "^0.4.2",
     "node-sass": "^4.9.3",
     "webpack": "^4.17.1",
     "webpack-cli": "^3.1.0",