fixed service YML code

Resources/doc/tutorial/creating_your_first_admin_class/defining_admin_class.rst

@@ -46,9 +46,9 @@ Or if you're using an YML configuration file,
     services:
        sonata.news.admin.post:
           class: Sonata\NewsBundle\Admin\PostAdmin
-       tags:
-         - { name: sonata.admin, manager_type: orm, group: sonata_blog, label: post }
-       arguments: [Sonata\NewsBundle\Entity\Post, SonataNewsBundle:PostAdmin]
+          tags:
+            - { name: sonata.admin, manager_type: orm, group: sonata_blog, label: post }
+          arguments: [Sonata\NewsBundle\Entity\Post, SonataNewsBundle:PostAdmin]
 
 
 These is the minimal configuration required to display the entity inside the dashboard and