chore(package): update webpack-dev-server to version 3.1.9 (#398)

quickly tested, seems to work fine

package.json

@@ -96,7 +96,7 @@
     "underscore-template-loader": "^1.0.0",
     "webpack": "^4.18.1",
     "webpack-cli": "^3.0.8",
-    "webpack-dev-server": "3.1.7",
+    "webpack-dev-server": "3.1.9",
     "webpack-merge": "^4.1.2",
     "webpack-visualizer-plugin": "^0.1.11"
   },