Bump webpack from 4.38.0 to 4.39.1 in /js

Bumps [webpack](https://github.com/webpack/webpack) from 4.38.0 to 4.39.1.
- [Release notes](https://github.com/webpack/webpack/releases)
- [Commits](https://github.com/webpack/webpack/compare/v4.38.0...v4.39.1)

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

js/package.json

@@ -40,7 +40,7 @@
     "vue-loader": "^15.7.1",
     "vue-style-loader": "^4.1.2",
     "vue-template-compiler": "^2.6.10",
-    "webpack": "^4.38.0",
+    "webpack": "^4.39.1",
     "webpack-cli": "^3.3.6",
     "webpack-merge": "^4.2.1"
   },