Fix RabbitMQJob

Fix for
```
In RabbitMQJob.php line 7:
                                                                               
  Declaration of DesignMyNight\Laravel\Horizon\Jobs\RabbitMQJob::delete() mus  
  t be compatible with VladimirYuldashev\LaravelQueueRabbitMQ\Queue\Jobs\Rabb  
  itMQJob::delete(): void    
```

Author: Walter Galvão

src/Jobs/RabbitMQJob.php

@@ -9,7 +9,7 @@ class RabbitMQJob extends BaseJob
     /**
      * {@inheritdoc}
      */
-    public function delete()
+    public function delete(): void
     {
         parent::delete();