minor #6003 #5999 fix files names (vincentaubert)

This PR was merged into the 2.3 branch.

Discussion
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#5999 fix files names

Fixes #5999

Commits
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7a9c1d7 #5999 fix files names

book/service_container.rst

@@ -109,15 +109,15 @@ be specified in YAML, XML or PHP:
 
     .. code-block:: yaml
 
-        # app/config/config.yml
+        # app/config/services.yml
         services:
             my_mailer:
                 class:        Acme\HelloBundle\Mailer
                 arguments:    [sendmail]
 
     .. code-block:: xml
 
-        <!-- app/config/config.xml -->
+        <!-- app/config/services.xml -->
         <?xml version="1.0" encoding="UTF-8" ?>
         <container xmlns="http://symfony.com/schema/dic/services"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
@@ -133,7 +133,7 @@ be specified in YAML, XML or PHP:
 
     .. code-block:: php
 
-        // app/config/config.php
+        // app/config/services.php
         use Symfony\Component\DependencyInjection\Definition;
 
         $container->setDefinition('my_mailer', new Definition(