Merge pull request #1961 from divine/fix_failed_job_exception

[Fix] Format exception to string in failed jobs

src/Jenssegers/Mongodb/Queue/Failed/MongoFailedJobProvider.php

@@ -12,12 +12,15 @@ class MongoFailedJobProvider extends DatabaseFailedJobProvider
      * @param string $connection
      * @param string $queue
      * @param string $payload
+     * @param  \Exception  $exception
      * @return void
      */
     public function log($connection, $queue, $payload, $exception)
     {
         $failed_at = Carbon::now()->getTimestamp();
 
+        $exception = (string) $exception;
+
         $this->getTable()->insert(compact('connection', 'queue', 'payload', 'failed_at', 'exception'));
     }