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

vendor/symfony/validator/Constraints/TrueValidator.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\Validator\Constraints;
+
+@trigger_error('The '.__NAMESPACE__.'\TrueValidator class is deprecated since version 2.7 and will be removed in 3.0. Use the IsTrueValidator class in the same namespace instead.', E_USER_DEPRECATED);
+
+/**
+ * @author Bernhard Schussek <bschussek@gmail.com>
+ *
+ * @deprecated since version 2.7, to be removed in 3.0. Use IsTrueValidator instead.
+ */
+class TrueValidator extends IsTrueValidator
+{
+}