Add reference to Async.legacy
Add reference to Async.legacy

Async.legacy adds support for OS 7 and OS X 10.9
alvinvarghese/Async,silan-liu/Async,tonyxiao/Async,A-Zak/Async,kostiakoval/Async,fullstackclub/Async,msdgwzhy6/Async,zhaoguohui/Async,zhaoguohui/Async,2h4u/Async,silan-liu/Async,A-Zak/Async,alvinvarghese/Async,csjlengxiang/Async,thedamfr/Async,hanhailong/Async,harlanhaskins/Async,harlanhaskins/Async,mihirpmehta/Async,0angelic0/Async,kostiakoval/Async,JohnCoates/Async,0angelic0/Async,0angelic0/Async,2h4u/Async,paterson/Async,TrainingPair/Async,alvinvarghese/Async,TrainingPair/Async,msdgwzhy6/Async,morizotter/Async,JohnCoates/Async,fullstackclub/Async,A-Zak/Async,tonyxiao/Async,0angelic0/Async,duemunk/Async,silan-liu/Async,csjlengxiang/Async,msdgwzhy6/Async,csjlengxiang/Async,zhaoguohui/Async,fullstackclub/Async,hanhailong/Async,silan-liu/Async,tonyxiao/Async,harlanhaskins/Async,paterson/Async,mihirpmehta/Async,thedamfr/Async,kostiakoval/Async,TrainingPair/Async,TrainingPair/Async,2h4u/Async,hanhailong/Async,morizotter/Async,A-Zak/Async,thedamfr/Async,csjlengxiang/Async,zhaoguohui/Async,msdgwzhy6/Async,alvinvarghese/Async,morizotter/Async,duemunk/Async,paterson/Async,tonyxiao/Async,mihirpmehta/Async,duemunk/Async,fullstackclub/Async,paterson/Async,JohnCoates/Async,morizotter/Async,hanhailong/Async,harlanhaskins/Async,mihirpmehta/Async