chore(package): update webpack to version 4.5.0

Closes #4

Author: greenkeeper[bot]

package.json

@@ -51,6 +51,6 @@
     "react": "^16.2.0",
     "react-dom": "^16.2.0",
     "react-test-renderer": "^16.2.0",
-    "webpack": "^3.0.0"
+    "webpack": "^4.5.0"
   }
 }