bump to 3.6.1+4

CHANGELOG.md

+# 3.6.1+4
+* Android P support
+
 # 3.6.1+3
 * Fix #431
 

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: 3.6.1+3
+version: 3.6.1+4
 homepage: https://github.com/JarvanMo/fluwx
 
 environment: