Bump webpack-dev-server from 4.11.1 to 4.12.0 in /amigo_mobile_ui (#303)

Bumps [webpack-dev-server](https://github.com/webpack/webpack-dev-server) from 4.11.1 to 4.12.0.
- [Release notes](https://github.com/webpack/webpack-dev-server/releases)
- [Changelog](https://github.com/webpack/webpack-dev-server/blob/master/CHANGELOG.md)
- [Commits](webpack/webpack-dev-server@v4.11.1...v4.12.0)

---
updated-dependencies:
- dependency-name: webpack-dev-server
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

amigo_mobile_ui/package-lock.json

@@ -19,7 +19,7 @@
     "url-loader": "^4.1.0",
     "webpack": "^4.0.0",
     "webpack-cli": "^4.0.0",
-    "webpack-dev-server": "^4.11.1"
+    "webpack-dev-server": "^4.12.0"
   },
   "dependencies": {
     "bootstrap": "^3.3.7",