Bump extract-text-webpack-plugin from 2.1.2 to 3.0.2 in /pkg/ui

Bumps [extract-text-webpack-plugin](https://github.com/webpack-contrib/extract-text-webpack-plugin) from 2.1.2 to 3.0.2.
- [Release notes](https://github.com/webpack-contrib/extract-text-webpack-plugin/releases)
- [Changelog](https://github.com/webpack-contrib/extract-text-webpack-plugin/blob/master/CHANGELOG.md)
- [Commits](webpack-contrib/extract-text-webpack-plugin@v2.1.2...v3.0.2)

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

pkg/ui/package.json

@@ -23,7 +23,7 @@
     "@types/webpack-env": "^1.13.0",
     "awesome-typescript-loader": "^3.2.1",
     "css-loader": "^2.1.1",
-    "extract-text-webpack-plugin": "^2.1.2",
+    "extract-text-webpack-plugin": "^3.0.2",
     "file-loader": "^0.11.2",
     "html-loader": "^0.4.5",
     "html-webpack-plugin": "^2.29.0",