Update dependency webpack-dev-server to v3.7.1 (GoogleChromeLabs#607)

Update dependency webpack-dev-server to v3.7.1

Author: surma

package-lock.json

@@ -70,7 +70,7 @@
     "webpack": "4.28.0",
     "webpack-bundle-analyzer": "3.3.2",
     "webpack-cli": "3.3.4",
-    "webpack-dev-server": "3.4.1",
+    "webpack-dev-server": "3.7.1",
     "worker-plugin": "3.1.0"
   }
 }