Bump webpack from 4.28.3 to 4.28.4 in /js

Bumps [webpack](https://github.com/webpack/webpack) from 4.28.3 to 4.28.4.
- [Release notes](https://github.com/webpack/webpack/releases)
- [Commits](https://github.com/webpack/webpack/compare/v4.28.3...v4.28.4)

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

js/package.json

@@ -30,7 +30,7 @@
     "karma": "^3.1.4",
     "mini-css-extract-plugin": "^0.5.0",
     "uglifyjs-webpack-plugin": "^2.1.1",
-    "webpack": "^4.28.3",
+    "webpack": "^4.28.4",
     "webpack-cli": "^3.2.0",
     "webpack-merge": "^4.2.1"
   },