bump to 3.13.1

CHANGELOG.md

+# 3.13.1
+* 分享到小程序的thumbnail为必填
+
 # 3.13.0
 * Android SDK升级到6.8.24
 * Kotlin升级到1.7.10

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: 3.13.0
+version: 3.13.1
 homepage: https://github.com/JarvanMo/fluwx
 
 environment: