Bump webpack-merge from 4.2.2 to 5.0.9

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](https://github.com/survivejs/webpack-merge/compare/v4.2.2...v5.0.9)

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

package.json

@@ -17,7 +17,7 @@
     "popper.js": "^1.16.1",
     "underscore": "^1.10.2",
     "vis": "^4.21.0",
-    "webpack-merge": "^4.2.2"
+    "webpack-merge": "^5.0.9"
   },
   "devDependencies": {
     "webpack-dev-server": "^3.11.0"