Bump webpack from 4.39.3 to 4.40.0 in /app (#207)

Bumps [webpack](https://github.com/webpack/webpack) from 4.39.3 to 4.40.0.
- [Release notes](https://github.com/webpack/webpack/releases)
- [Commits](webpack/webpack@v4.39.3...v4.40.0)

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

Author: dependabot-preview[bot]

app/package-lock.json

@@ -22,7 +22,7 @@
     "postcss-import": "^12.0.1",
     "postcss-loader": "^3.0.0",
     "style-loader": "^1.0.0",
-    "webpack": "^4.39.3",
+    "webpack": "^4.40.0",
     "webpack-cli": "^3.3.8"
   },
   "scripts": {