chore(package): update webpack-dev-server to version 3.1.0

Closes #41

Author: greenkeeper[bot]

package.json

@@ -85,7 +85,7 @@
     "ts-node": "^3.0.6",
     "typescript": "^2.4.1",
     "webpack": "^3.0.0",
-    "webpack-dev-server": "^2.5.0",
+    "webpack-dev-server": "^3.1.0",
     "webpack-node-externals": "^1.6.0",
     "webpack-stats-plugin": "^0.1.5",
     "yaml-import-loader": "^1.3.3",