chore(package): update copy-webpack-plugin to version 6.0.1

Closes #345

Author: greenkeeper[bot]

package.json

@@ -55,7 +55,7 @@
     "babel-register": "^6.24.0",
     "babel-runtime": "^6.11.6",
     "chai": "^4.0.2",
-    "copy-webpack-plugin": "^4.0.1",
+    "copy-webpack-plugin": "^6.0.1",
     "core-js": "^2.4.1",
     "cross-env": "^5.0.1",
     "css-loader": "^0.28.0",