Update override_dir_structure.rst

Added new line to make code-block work

Author: marcel-burkhard

cookbook/configuration/override_dir_structure.rst

@@ -151,5 +151,6 @@ the ``extra.symfony-web-dir`` option in the ``composer.json`` file:
     work:
 
     .. code-block:: bash
+    
         $ php app/console cache:clear --env=prod
         $ php app/console assetic:dump --env=prod --no-debug