Bump webpack-dev-server from 2.11.3 to 3.1.11

Bumps [webpack-dev-server](https://github.com/webpack/webpack-dev-server) from 2.11.3 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@v2.11.3...v3.1.11)

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

Author: dependabot[bot]

package.json

@@ -50,7 +50,7 @@
     "sw-precache-webpack-plugin": "0.11.4",
     "url-loader": "0.6.2",
     "webpack": "3.8.1",
-    "webpack-dev-server": "2.11.3",
+    "webpack-dev-server": "3.1.11",
     "webpack-manifest-plugin": "1.3.2",
     "whatwg-fetch": "2.0.3"
   },