update QA.md

doc/BASIC_KNOWLEDGE.md

@@ -5,8 +5,8 @@ Actually, almost every result from functions like `shareToWeChat` or `payWithWeC
 So if you want get the real result you shall do like this:
 
 ```dart
-  weChatResponseEventHandler.listen((res) {
-      if (res is WeChatPaymentResponse) {
+  fluwx.weChatResponseEventHandler.listen((res) {
+    if (res is fluwx.WeChatPaymentResponse) {
       // do something here
     }
   });

doc/BASIC_KNOWLEDGE_CN.md

@@ -6,8 +6,8 @@
 为了获取真实的回调，你应该这样做：
 
 ```dart
-  weChatResponseEventHandler.listen((res) {
-      if (res is WeChatPaymentResponse) {
+  fluwx.weChatResponseEventHandler.listen((res) {
+    if (res is fluwx.WeChatPaymentResponse) {
       // do something here
     }
   });