add use statement

Author: erlangparasu

components/mailer.rst

@@ -66,6 +66,7 @@ it:
 Then, use the SMTP Gmail transport::
 
     use Symfony\Component\Mailer\Bridge\Google\Smtp\GmailTransport;
+    use Symfony\Component\Mailer\Mailer;
 
     $transport = new GmailTransport('user', 'pass');
     $mailer = new Mailer($transport);