Bump webpack from 4.14.0 to 4.15.1 in /js

Bumps [webpack](https://github.com/webpack/webpack) from 4.14.0 to 4.15.1.
- [Release notes](https://github.com/webpack/webpack/releases)
- [Commits](https://github.com/webpack/webpack/compare/v4.14.0...v4.15.1)

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

js/package.json

@@ -28,7 +28,7 @@
     "karma": "^2.0.4",
     "mini-css-extract-plugin": "^0.4.1",
     "node-sass": "^4.9.2",
-    "webpack": "^4.14.0",
+    "webpack": "^4.15.1",
     "webpack-cli": "^3.0.8",
     "webpack-merge": "^4.1.3"
   },