chore(package): update webpack to version 4.1.0

Closes #6

Author: greenkeeper[bot]

package.json

@@ -39,7 +39,7 @@
     "mocha": "^4.0.0",
     "nyc": "^11.1.0",
     "rimraf": "^2.6.1",
-    "webpack": "^3.5.4",
+    "webpack": "^4.1.0",
     "yaml-loader": "^0.5.0"
   }
 }