Improved example in transactions.mdx

This is the kind of thing the `finally` block was inveted for, to release resources and things like that.

Author: adriancuadrado

docs/pages/features/transactions.mdx

@@ -31,10 +31,10 @@ try {
   const insertPhotoValues = [res.rows[0].id, 's3.bucket.foo']
   await client.query(insertPhotoText, insertPhotoValues)
   await client.query('COMMIT')
-  client.release()
 } catch (e) {
   await client.query('ROLLBACK')
-  client.release()
   throw e
+} finally {
+  client.release()
 }
 ```