bump to 3.1.0-nullsafety.2

CHANGELOG.md

-## 3.1.0-nullsafety.1
+## 3.1.0-nullsafety.2
+* Nothing
+
+## 3.1.0-nullsafety.2
 * Android支持通过H5冷启动app传递<wx-open-launch-app>中的extinfo数据
 * Android新加<meta-data>handleWeChatRequestByFluwx</meta-data>。
 

pubspec.yaml

 name: fluwx
 description: The capability of implementing WeChat SDKs in Flutter. With Fluwx, developers can use WeChatSDK easily, such as sharing, payment, lanuch mini program and etc.
-version: 3.1.0-nullsafety.1
+version: 3.1.0-nullsafety.2
 homepage: https://github.com/JarvanMo/fluwx
 
 environment: