code: function es6ToEs5(input, output, proName) {
      task.src(input)
          .pipe(plumberPlugin())
          .pipe(taskIf(config.target === 'ES6', streamPlugin(webConfig)))
          .pipe(renamePlugin(`${proName}.min.js`))
          .pipe(replacePlugin('@@replace', config.replaceStr || ''))
          .pipe(connectPlugin.reload())
          .pipe(task.dest(output));
  }
docs: 更具项目来判断是否进行es6的转换
  @param input
  @param output
  @param proName