Update serializer.rst

Author: atailouloute

serializer.rst

@@ -305,7 +305,7 @@ value:
         $container->loadFromExtension('framework', array(
             // ...
             'serializer' => array(
-                'name_converter' => 'serializer.name_converter.camel_case_to_snake_case,
+                'name_converter' => 'serializer.name_converter.camel_case_to_snake_case',
             ),
         ));