Update models.md

Incorrect syntax.

documents/models.md

@@ -164,7 +164,7 @@ Save records having `UpdatedAt` field will set it to current time.
 
 ```go
 db.Save(&user) // will set `UpdatedAt` to current time
-db.Model(&user).Update("name", "jinzhu") // will set `UpdatedAt` to current time
+db.Model(&user).Update("UpdatedAt", time.Now()) // will set `UpdatedAt` to current time
 ```
 
 ### Use `DeletedAt` to store record's deleted time if field exists