readme: add correction in the "Multiple updates in one query" section

Correct the "returning" clause.

Author: paulovieira

README.md

@@ -245,7 +245,7 @@ sql`
   update users set name = update_data.name, (age = update_data.age)::int
   from (values ${sql(users)}) as update_data (id, name, age)
   where users.id = (update_data.id)::int
-  returning users.id, users.sort_order
+  returning users.id, users.name, users.age
 `
 ```