chore(package): update copy-webpack-plugin to version 5.1.1

Closes #28

Author: greenkeeper[bot]

package.json

@@ -19,7 +19,7 @@
     }
   },
   "devDependencies": {
-    "copy-webpack-plugin": "^4.6.0",
+    "copy-webpack-plugin": "^5.1.1",
     "eslint": "^4.5.0",
     "eslint-config-developit": "^1.1.1",
     "preact-cli": "^3.0.0-next.14",