code: function(url, options, fn){
          var r = request.post(url, fn);
          var form = r.form();
          form.append('field', options.field);
          form.append('files', fs.createReadStream(options.filepath));
          return form;
      }
docs: 模拟Form表单上传
  @param   {String|Object}   url|options   上传接口|Request.Options，参看request.api
  @param   {Object}          options       上传目标文件路径
  @param   {Function}        fn            回调函数