fix(package): update webpack to version 4.29.4

Closes #89

Author: greenkeeper[bot]

package.json

@@ -44,6 +44,6 @@
     "sass-loader": "^6.0.5",
     "standard": "^11.0.0",
     "style-loader": "^0.20.0",
-    "webpack": "^3.0.0"
+    "webpack": "^4.29.4"
   }
 }