chore(package): update webpack to version 4.0.0

Author: greenkeeper[bot]

Diff for: package.json

@@ -36,7 +36,7 @@
     "mocha": "^4.0.1",
     "mocha-lcov-reporter": "^1.2.0",
     "recursive-readdir-sync": "^1.0.6",
-    "webpack": "^3.5.2",
+    "webpack": "^4.0.0",
     "mockery": "^2.1.0"    
   }
 }