Update to Drupal 8.1.7. For more information, see https://www.drupal.org/project/drupal/releases/8.1.7

vendor/guzzlehttp/promises/src/TaskQueue.php

@@ -56,6 +56,7 @@ class TaskQueue
      */
     public function run()
     {
+        /** @var callable $task */
         while ($task = array_shift($this->queue)) {
             $task();
         }