Update messaging.md

Author: yang-xiaodong

docs/content/user-guide/en/cap/messaging.md

@@ -99,7 +99,7 @@ The following is the content that needs to be written into the header of the mes
 
  | Key           | DataType | Description                                                    |
  | ------------- | -------- | -------------------------------------------------------------- |
- | cap-msg-id    | string   | Message Id, Generated by snowflake algorithm, can also be guid |
+ | cap-msg-id    | long     | Message Id, Generated by snowflake algorithm                   |
  | cap-msg-name  | string   | The name of the message                                        |
  | cap-msg-type  | string   | The type of message, `typeof(T).FullName`(not required)        |
  | cap-senttime  | string   | sending time (not required)                                    |