minor #575 Showcase short definition syntax (ogizanagi, javiereguiluz)

This PR was merged into the master branch.

Discussion
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Showcase short definition syntax

Commits
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f857b2f Tweaked the help note
fcca1cb Showcase short definition syntax

app/config/services.yml

@@ -30,18 +30,17 @@ services:
         arguments:
             $emailSender: '%app.notifications.email_sender%'
 
+    # when the service definition only contains arguments, you can omit the
+    # 'arguments' key and define the arguments just below the service class
     AppBundle\Twig\AppExtension:
-        arguments:
-            $locales: '%app_locales%'
+        $locales: '%app_locales%'
 
     AppBundle\EventListener\CommentNotificationSubscriber:
-        arguments:
-            $sender: '%app.notifications.email_sender%'
+        $sender: '%app.notifications.email_sender%'
 
     AppBundle\EventListener\RedirectToPreferredLocaleSubscriber:
-        arguments:
-            $locales: '%app_locales%'
-            $defaultLocale: '%locale%'
+        $locales: '%app_locales%'
+        $defaultLocale: '%locale%'
 
     # needed for the localizeddate Twig filter
     Twig\Extensions\IntlExtension: ~