Fix typo (#148)

Author: shenli

sql/mysql-compatibility.md

@@ -67,7 +67,7 @@ TiDB implements the asynchronous schema changes algorithm in F1. The Data Manipu
 
 ### Transaction
 
-TiDB implementsa an optimistic transaction model. Unlike MySQL, which uses row-level locking to avoid write conflict, in TiDB, the write conflict is checked only in the `commit` process during the execution of the statements like `Update`, `Insert`, `Delete`, and so on. 
+TiDB implements an optimistic transaction model. Unlike MySQL, which uses row-level locking to avoid write conflict, in TiDB, the write conflict is checked only in the `commit` process during the execution of the statements like `Update`, `Insert`, `Delete`, and so on. 
 
 **Note:** On the business side, remember to check the returned results of `commit` because even there is no error in the execution, there might be errors in the `commit` process.