Bump webpack-dev-server from 2.11.2 to 3.1.11

Bumps [webpack-dev-server](https://github.com/webpack/webpack-dev-server) from 2.11.2 to 3.1.11.
- [Release notes](https://github.com/webpack/webpack-dev-server/releases)
- [Changelog](https://github.com/webpack/webpack-dev-server/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack/webpack-dev-server/compare/v2.11.2...v3.1.11)

package.json

@@ -10,6 +10,6 @@
     "stimulus": "^1.1.0"
   },
   "devDependencies": {
-    "webpack-dev-server": "2.11.2"
+    "webpack-dev-server": "3.1.11"
   }
 }