Fixed typo in json error template

src/Symfony/Bundle/FrameworkBundle/Resources/views/Exception/error.json.twig

@@ -1 +1 @@
-{{ { 'error': { 'code': status_code, 'message': status_text } }|json_encode }}
+{{ { 'error': { 'code': status_code, 'message': status_text } }|json_encode|raw }}