bump to 2.0.0

pubspec.yaml

 name: fluwx
 description: A implement of WeChatSDK on Flutter.Let's make it easier with Fluwx.
-version: 0.1.9
+version: 0.2.0
 author: JarvanMo <jarvan.mo@gmail.com>
 homepage: https://github.com/JarvanMo/fluwx