use api 21 emulator for travis tests
use api 21 emulator for travis tests

grandcentrix/tray,extinguish/tray,suzukaze/tray,whittmy/tray,bin-liu/tray,ravishankeraquevix/tray,omegasoft7/tray,qwe3243002/tray,MaTriXy/tray,passsy/tray,sdjtu502/tray,wtttc/tray,mistrydarshan99/tray,freakynit/tray,draekko/tray