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

vendor/symfony/dependency-injection/Tests/Fixtures/containers/container14.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace Container14;
+
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+
+/**
+ * This file is included in Tests\Dumper\GraphvizDumperTest::testDumpWithFrozenCustomClassContainer
+ * and Tests\Dumper\XmlDumperTest::testCompiledContainerCanBeDumped.
+ */
+if (!class_exists('Container14\ProjectServiceContainer')) {
+    class ProjectServiceContainer extends ContainerBuilder
+    {
+    }
+}
+
+return new ProjectServiceContainer();