Update dependency webpack to v4.28.1

Author: renovate-bot

package-lock.json

@@ -52,7 +52,7 @@
     "prettier": "1.13.7",
     "stats-webpack-plugin": "0.7.0",
     "url-join": "4.0.0",
-    "webpack": "4.26.0",
+    "webpack": "4.28.1",
     "webpack-node-externals": "1.7.2"
   },
   "peerDependencies": {