修改了async的注释 [Doc]在async的API中隐藏了Deferred类
修改了async的注释
[Doc]在async的API中隐藏了Deferred类

Signed-off-by: 徐振华 <85a53bbb11779b0583cb14f7a4a13b31601047fb@gmail.com>

BaiduFE/Tangram-base,BaiduFE/Tangram-base,BaiduFE/Tangram-base