Use constants instead of numbers to set email priority

Author: javiereguiluz

components/mime.rst

@@ -44,13 +44,14 @@ methods to compose the entire email message::
 
     use Symfony\Component\Mime\Email;
 
+
     $email = (new Email())
         ->from('[email protected]')
         ->to('[email protected]')
         ->cc('[email protected]')
         ->bcc('[email protected]')
         ->replyTo('[email protected]')
-        ->priority(1)
+        ->priority(Email::PRIORITY_HIGH)
         ->subject('Important Notification')
         ->text('Lorem ipsum...')
         ->html('<h1>Lorem ipsum</h1> <p>...</p>')