upgraded proguard to 5.2
upgraded proguard to 5.2

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