Chunk.entrypoints: Use Chunks.groupsIterable and filter by instanceof Entrypoint instead

如题报错是因为webpack用了4以上版本 ，而extract-text-webpack-plugin过低造成的。解决办法升级extract-text-webpack-plugin或降级webpack。

升级extract-text-webpack-plugin：

npm install extract-text-webpack-plugin@next --save-dev