class attribute still needed in some cases

The class attribute is still needed for non namespaced classes like Twig_Extensions_Extension_Intl

Author: florian987

reference/dic_tags.rst

@@ -1264,6 +1264,7 @@ also have to be added as regular services:
 
         services:
             Twig_Extensions_Extension_Intl:
+                class: Twig_Extensions_Extension_Intl
                 tags: [twig.extension]
 
     .. code-block:: xml
@@ -1275,7 +1276,7 @@ also have to be added as regular services:
                 http://symfony.com/schema/dic/services/services-1.0.xsd">
 
             <services>
-                <service id="Twig_Extensions_Extension_Intl">
+                <service id="Twig_Extensions_Extension_Intl" class="Twig_Extensions_Extension_Intl">
                     <tag name="twig.extension" />
                 </service>
             </services>
@@ -1284,7 +1285,7 @@ also have to be added as regular services:
     .. code-block:: php
 
         $container
-            ->register('Twig_Extensions_Extension_Intl')
+            ->register('Twig_Extensions_Extension_Intl', Twig_Extensions_Extension_Intl::class)
             ->addTag('twig.extension')
         ;