Bump webpack from 4.36.1 to 4.39.2

Bumps [webpack](https://github.com/webpack/webpack) from 4.36.1 to 4.39.2.
- [Release notes](https://github.com/webpack/webpack/releases)
- [Commits](webpack/webpack@v4.36.1...v4.39.2)

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Signed-off-by: npmbuildbot[bot] <npmbuildbot[bot]@users.noreply.github.com>

Author: dependabot-preview[bot]

js/notifications.js

@@ -43,7 +43,7 @@
     "sass-loader": "^7.1.0",
     "vue-loader": "^15.7.1",
     "vue-template-compiler": "^2.6.10",
-    "webpack": "^4.36.1",
+    "webpack": "^4.39.2",
     "webpack-cli": "^3.3.6",
     "webpack-merge": "^4.2.1"
   }