upgraded proguard to 5.2.1
upgraded proguard to 5.2.1

jasonchaffee/moco,yonglehou/moco,cgourlay/moco,ruiruiguo/moco,yonglehou/moco,ForrestAlfred/moco,ysjian/moco,dreamhead/moco,ForrestVV/moco,LiuShulong/moco,sandyway/moco,LiuShulong/moco,dreamhead/moco,cgourlay/moco,jasonchaffee/moco,ruiruiguo/moco,zhigang1992/moco,ForrestVV/moco,zhigang1992/moco,sandyway/moco,ForrestAlfred/moco,ysjian/moco