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)

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

package.json

@@ -64,7 +64,7 @@
     "url-loader": "0.6.2",
     "web3": "1.0.0-beta.34",
     "webpack": "3.12.0",
-    "webpack-dev-server": "2.11.2",
+    "webpack-dev-server": "3.1.11",
     "webpack-manifest-plugin": "1.3.2",
     "whatwg-fetch": "2.0.3"
   },