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

vendor/symfony/console/Output/BufferedOutput.php

@@ -0,0 +1,48 @@
+<?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\Console\Output;
+
+/**
+ * @author Jean-François Simon <contact@jfsimon.fr>
+ */
+class BufferedOutput extends Output
+{
+    /**
+     * @var string
+     */
+    private $buffer = '';
+
+    /**
+     * Empties buffer and returns its content.
+     *
+     * @return string
+     */
+    public function fetch()
+    {
+        $content = $this->buffer;
+        $this->buffer = '';
+
+        return $content;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function doWrite($message, $newline)
+    {
+        $this->buffer .= $message;
+
+        if ($newline) {
+            $this->buffer .= "\n";
+        }
+    }
+}