Update to drupal 8.0.0-rc1. For more information, see https://www.drupal.org/node/2582663

vendor/symfony/serializer/Tests/Fixtures/TraversableDummy.php

@@ -0,0 +1,23 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Serializer\Tests\Fixtures;
+
+class TraversableDummy implements \IteratorAggregate
+{
+    public $foo = 'foo';
+    public $bar = 'bar';
+
+    public function getIterator()
+    {
+        return new \ArrayIterator(get_object_vars($this));
+    }
+}