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

vendor/symfony/dependency-injection/Tests/Fixtures/containers/container8.php

@@ -0,0 +1,14 @@
+<?php
+
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\ParameterBag\ParameterBag;
+
+$container = new ContainerBuilder(new ParameterBag(array(
+    'FOO' => '%baz%',
+    'baz' => 'bar',
+    'bar' => 'foo is %%foo bar',
+    'escape' => '@escapeme',
+    'values' => array(true, false, null, 0, 1000.3, 'true', 'false', 'null'),
+)));
+
+return $container;