fix: [doc] Use the Mailer component instead of SwiftMailer (#1488)

Author: mdoutreluingne

core/events.md

@@ -90,12 +90,14 @@ use Symfony\Component\EventDispatcher\EventSubscriberInterface;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpKernel\Event\ViewEvent;
 use Symfony\Component\HttpKernel\KernelEvents;
+use Symfony\Component\Mime\Email;
+use Symfony\Component\Mailer\MailerInterface;
 
 final class BookMailSubscriber implements EventSubscriberInterface
 {
     private $mailer;
 
-    public function __construct(\Swift_Mailer $mailer)
+    public function __construct(MailerInterface $mailer)
     {
         $this->mailer = $mailer;
     }
@@ -116,10 +118,11 @@ final class BookMailSubscriber implements EventSubscriberInterface
             return;
         }
 
-        $message = (new \Swift_Message('A new book has been added'))
-            ->setFrom('[email protected]')
-            ->setTo('[email protected]')
-            ->setBody(sprintf('The book #%d has been added.', $book->getId()));
+        $message = (new Email())
+            ->from('[email protected]')
+            ->to('[email protected]')
+            ->subject('A new book has been added')
+            ->text(sprintf('The book #%d has been added.', $book->getId()));
 
         $this->mailer->send($message);
     }