fix(package): update copy-webpack-plugin to version 4.2.1

Author: greenkeeper[bot]

package.json

@@ -70,7 +70,7 @@
     "c3": "0.4.18",
     "chalk": "2.2.2",
     "clean-webpack-plugin": "0.1.17",
-    "copy-webpack-plugin": "4.2.0",
+    "copy-webpack-plugin": "4.2.1",
     "core-js": "2.5.1",
     "css-loader": "0.28.6",
     "d3": "3.5.17",