bump to 3.8.1

CHANGELOG.md

-# 3.8.0+1
+# 3.8.1
+* 在iOS中增加FluwxDelegate
+* 尝试修复iOS冷启动获取extMsg问题
+
+# 3.8.0+2
 * Fix #461
 
 # 3.8.0

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: 3.8.0+1
+version: 3.8.1
 homepage: https://github.com/JarvanMo/fluwx
 
 environment: