code: function _createFileTask(gulp, name, config, depTasks, index, startFun, endFun) {
      gulp.task(name, depTasks, function(){
          var s = config.files[index];
         return runFileTaskStream(gulp, s, config, startFun, endFun);
      });
  }
docs: 借用闭包，处理gulp的task中index