build(deps-dev): bump webpack-merge from 4.2.2 to 5.2.0 in /frontend (#629)

Bumps [webpack-merge](https://github.com/survivejs/webpack-merge) from 4.2.2 to 5.2.0.
- [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...v5.2.0)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

frontend/package.json

@@ -48,7 +48,7 @@
     "webpack": "^4.40.2",
     "webpack-cli": "^4.0.0",
     "webpack-dev-server": "^3.7.2",
-    "webpack-merge": "^4.2.1"
+    "webpack-merge": "^5.2.0"
   },
   "dependencies": {
     "chartist": "^0.11.3",