Bump webpack-dev-server from 2.9.4 to 3.1.11

Bumps [webpack-dev-server](https://github.com/webpack/webpack-dev-server) from 2.9.4 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](webpack/webpack-dev-server@v2.9.4...v3.1.11)

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

Author: dependabot[bot]

package.json

@@ -41,7 +41,7 @@
     "vhost": "^3.0.0",
     "webpack": "^3.8.1",
     "webpack-dev-middleware": "^1.12.0",
-    "webpack-dev-server": "^2.9.4",
+    "webpack-dev-server": "^3.1.11",
     "webpack-md5-hash": "0.0.5",
     "webpack-strip": "^0.1.0"
   },