chore(package): update workbox-webpack-plugin to version 4.1.0

Closes #335

Author: greenkeeper[bot]

package.json

@@ -72,7 +72,7 @@
     "webpack": "4.29.5",
     "webpack-cli": "3.2.3",
     "webpack-dev-server": "3.1.14",
-    "workbox-webpack-plugin": "3.6.3",
+    "workbox-webpack-plugin": "4.1.0",
     "xo": "0.24.0"
   },
   "dependencies": {