chunks

默认是 ['umi']，可修改，比如做了 vendors 依赖提取之后，会需要在 umi.js 之前加载 vendors.js。

比如：

export default {
  chunks: ['vendors', 'umi']
  chainWebpack: function (config, { webpack }) {
    config.merge({
      optimization: {
        minimize: true,
        splitChunks: {
          chunks: 'all',
          minSize: 30000,
          minChunks: 3,
          automaticNameDelimiter: '.',
          cacheGroups: {
            vendor: {
              name: 'vendors',
              test({ resource }) {
                return /[\\/]node_modules[\\/]/.test(resource);
              },
              priority: 10,
            },
          },
        },
      }
    });
  },
}