Fix EventType comment.

[chenyun]

No description provided.

[shyiko]

Fixed EventHeaderV4Deserializer eventLength handling is definitely "must merge". Thank you. Query event description on the other hand... I'd rather stick with the current one because there are some special-meaning queries like BEGIN/COMMIT which are not really updating anything on their own.
Would you care to open a separate PR for "fix EventHeaderV4Deserializer type bug"?

[chenyun]

Hi @shyiko ,
the QueryEvent comment I used is the same as MySQL document.
For "Represent query statement", I think it's ambiguous.
While "Written when an updating statement is done" means it's the first event of an updating statement.

Query :  Begin   
RowsQuery:   insert/update/delete sql  
TableMap :   
Rows :  Write/Update/DELETE  
Query/XId

Refer: https://dev.mysql.com/doc/internals/en/event-meanings.html

[shyiko]

Fair enough. Merging in.