add webpack-merge

Author: leaves4j

package-lock.json

@@ -50,6 +50,7 @@
     "null-loader": "^0.1.1",
     "serialize-javascript": "^1.3.0",
     "webpack": "^3.4.1",
+    "webpack-merge": "^4.1.0",
     "webpack-node-externals": "^1.6.0"
   },
   "peerDependencies": {