move copy-webpack-plugin to production dependencies

package.json

@@ -68,7 +68,6 @@
   },
   "devDependencies": {
     "babel-plugin-istanbul": "^4.0.0",
-    "copy-webpack-plugin": "^4.0.1",
     "eslint": "^3.10.1",
     "eslint-config-airbnb-base": "^10.0.1",
     "eslint-import-resolver-webpack": "^0.8.1",