Add DateTime to possible param types for $delay variable in queue abl…

…e delay function (#15826)

src/Illuminate/Bus/Queueable.php

@@ -54,7 +54,7 @@ public function onQueue($queue)
     /**
      * Set the desired delay for the job.
      *
-     * @param  int|null  $delay
+     * @param  \DateTime|int|null  $delay
      * @return $this
      */
     public function delay($delay)