release 3.1.0
release 3.1.0

35a4fe0 readme: update doc for `registerVoipToken` will fire cached token  ( zxcpoiu 2021-01-15 19:03:13 +0800)
bb5485b remove unused import  ( zxcpoiu 2021-01-15 18:44:22 +0800)
3d1b675 cache lastVoipToken and return it when subsequently call to registerVoipToken  ( zxcpoiu 2021-01-15 18:15:55 +0800)
ab54fd9 readme: update usage doc add some notes  ( zxcpoiu 2020-12-08 16:16:07 +0800)

ianlin/react-native-voip-push-notification,ianlin/react-native-voip-push-notification