Downgrade webpack-dev-server because of webpack/webpack-dev-server/issues/2029

Author: nya1

package.json

@@ -49,7 +49,7 @@
     "vue-template-compiler": "^2.5.2",
     "webpack": "^3.6.0",
     "webpack-bundle-analyzer": "^3.3.2",
-    "webpack-dev-server": "^3.1.11",
+    "webpack-dev-server": "2.9.7",
     "webpack-merge": "^4.1.0"
   },
   "engines": {