minor #4808 Email message instantiation changed to a more 'symfonysh' way. (alebo)

This PR was merged into the 2.3 branch.

Discussion
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Email message instantiation changed to a more 'symfonysh' way.

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets |

I believe that using a static factory method for instantiation isn't the best way to do it in Symfony. So I suggest updating the Sending Emails example.

Commits
-------

7f8b051 Changed email message instantiation to a more 'symfonysh' way.

Author: wouterj

cookbook/email/email.rst

@@ -103,7 +103,8 @@ an email is pretty straightforward::
 
     public function indexAction($name)
     {
-        $message = \Swift_Message::newInstance()
+        $mailer = $this->get('mailer');
+        $message = $mailer->createMessage()
             ->setSubject('Hello Email')
             ->setFrom('send@example.com')
             ->setTo('recipient@example.com')
@@ -114,7 +115,7 @@ an email is pretty straightforward::
                 )
             )
         ;
-        $this->get('mailer')->send($message);
+        $mailer->send($message);
 
         return $this->render(...);
     }