Bump webpack-dev-server from 2.11.2 to 3.1.11 (#134)

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

@@ -71,7 +71,7 @@
     "vue-template-compiler": "^2.5.2",
     "webpack": "^3.6.0",
     "webpack-bundle-analyzer": "^3.3.2",
-    "webpack-dev-server": "^2.9.1",
+    "webpack-dev-server": "^3.1.11",
     "webpack-merge": "^4.1.0"
   },
   "engines": {