[Reference] fix namespace in Expression constraint

Author: Christian Flothmann

reference/constraints/Expression.rst

@@ -73,7 +73,7 @@ One way to accomplish this is with the Expression constraint:
     .. code-block:: php-annotations
 
         // src/Acme/DemoBundle/Model/BlogPost.php
-        namespace Acme\DemoBundle\Model\BlogPost;
+        namespace Acme\DemoBundle\Model;
         
         use Symfony\Component\Validator\Constraints as Assert;
 
@@ -102,11 +102,10 @@ One way to accomplish this is with the Expression constraint:
             </constraint>
         </class>
 
-
     .. code-block:: php
 
         // src/Acme/DemoBundle/Model/BlogPost.php
-        namespace Acme\DemoBundle\Model\BlogPost;
+        namespace Acme\DemoBundle\Model;
         
         use Symfony\Component\Validator\Mapping\ClassMetadata;
         use Symfony\Component\Validator\Constraints as Assert;