bump to 5.3.1

CHANGELOG.md

+# 5.3.1
+* JVM target降低至11
+
 # 5.3.0
 * 升级kotlin、gradle相关
 * 更新progurad规则(#672)

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: 5.3.0
+version: 5.3.1
 homepage: https://github.com/OpenFlutter/fluwx
 
 environment: