chore(package): update webpack to version 4.33.0

Closes #259

Author: greenkeeper[bot]

package.json

@@ -57,7 +57,7 @@
     "remap-istanbul": "^0.11.1",
     "snazzy": "^7.1.0",
     "standard": "^9.0.0",
-    "webpack": "^3.0.0",
+    "webpack": "^4.33.0",
     "whatwg-fetch": "^2.0.3"
   },
   "repository": {