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

vendor/guzzlehttp/guzzle/src/Handler/CurlFactoryInterface.php

@@ -0,0 +1,27 @@
+<?php
+namespace GuzzleHttp\Handler;
+
+use Psr\Http\Message\RequestInterface;
+
+interface CurlFactoryInterface
+{
+    /**
+     * Creates a cURL handle resource.
+     *
+     * @param RequestInterface $request Request
+     * @param array            $options Transfer options
+     *
+     * @return EasyHandle
+     * @throws \RuntimeException when an option cannot be applied
+     */
+    public function create(RequestInterface $request, array $options);
+
+    /**
+     * Release an easy handle, allowing it to be reused or closed.
+     *
+     * This function must call unset on the easy handle's "handle" property.
+     *
+     * @param EasyHandle $easy
+     */
+    public function release(EasyHandle $easy);
+}