Fix XML mapping

Author: dunglas

components/serializer.rst

@@ -215,17 +215,17 @@ Then, create your groups definition:
     .. code-block:: xml
 
         <?xml version="1.0" ?>
-        <serializer xmlns="http://symfony.com/schema/dic/serializer"
+        <serializer xmlns="http://symfony.com/schema/dic/serializer-mapping"
                             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-                            xsi:schemaLocation="http://symfony.com/schema/dic/serializer http://symfony.com/schema/dic/constraint-mapping/serializer-1.0.xsd">
+                            xsi:schemaLocation="http://symfony.com/schema/dic/serializer-mapping http://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd">
             <class name="Acme\MyObj">
                 <attribute name="foo">
-                    <group name="group1" />
-                    <group name="group2" />
+                    <group>group1</group>
+                    <group>group2</group>
                 </attribute>
 
                 <attribute name="bar">
-                    <group name="group3" />
+                    <group>group3</group>
                 </attribute>
             </class>
         </serializer>