chore(package): update webpack to version 4.12.1

Closes #341

Author: greenkeeper[bot]

package.json

@@ -76,7 +76,7 @@
     "vue": "^2.5.16",
     "vue-loader": "^14.0.0",
     "vue-template-compiler": "^2.5.0",
-    "webpack": "^3.0.0",
+    "webpack": "^4.12.1",
     "webpack-dev-server": "^2.5.1",
     "webpack-merge": "^4.1.0",
     "whatwg-fetch": "^2.0.3"