MOD: update travis to xcode7
MOD: update travis to xcode7

Change-Id: I778c2b69b85317dba3e994d889ce488c5c6fe04d

raomengyun/YTKNetwork,raomengyun/YTKNetwork,wsxzk/YTKNetwork,jjj2mdd/YTKNetwork,skyline75489/YTKNetwork,jjj2mdd/YTKNetwork,yuantiku/YTKNetwork,thuai/YTKNetwork,KevinShawn/YTKNetwork