bump to 3.3.0

CHANGELOG.md

+## 3.3.0
+* Null-safety support
+* Fix #350
+
 ## 2.6.2
 * Fix #338 on Android
 

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: 3.2.2-nullsafety.1
+version: 3.3.0
 homepage: https://github.com/JarvanMo/fluwx
 
 environment: