Add lost backslash

Format is broken without the three backslasees

documents/models.md

@@ -166,6 +166,7 @@ Save records having `UpdatedAt` field will set it to current time.
 // Whenever one or more `user` fields are edited using Save() or Update(), `UpdatedAt` will be set to current time
 db.Save(&user) // will set `UpdatedAt` to current time
 db.Model(&user).Update("name", "jinzhu") // will set `UpdatedAt` to current time 
+```
 
 ### Use `DeletedAt` to store record's deleted time if field exists