add version shield icon

Author: Wonday

README.md

@@ -1,4 +1,6 @@
 # react-native-aliyun-push
+[![npm](https://img.shields.io/npm/v/react-native-aliyun-push.svg?style=flat-square)](https://www.npmjs.com/package/react-native-aliyun-push)
+
 [阿里云移动推送](https://www.aliyun.com/product/cps?spm=5176.2020520107.0.0.fgXGFp)react-native封装组件