build(deps-dev): Bump webpack-merge from 4.2.2 to 5.0.9 in /frontend

Bumps [webpack-merge](https://github.com/survivejs/webpack-merge) from 4.2.2 to 5.0.9.
- [Release notes](https://github.com/survivejs/webpack-merge/releases)
- [Changelog](https://github.com/survivejs/webpack-merge/blob/master/CHANGELOG.md)
- [Commits](survivejs/webpack-merge@v4.2.2...v5.0.9)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

frontend/package.json

@@ -48,7 +48,7 @@
     "webpack": "^4.40.2",
     "webpack-cli": "^3.3.6",
     "webpack-dev-server": "^3.7.2",
-    "webpack-merge": "^4.2.1"
+    "webpack-merge": "^5.0.9"
   },
   "dependencies": {
     "chartist": "^0.11.3",