title: Laravel multiple workers running job twice
body: <p>I am using Laravel 5.6 and I am dispatching jobs to a queue and then using supervisor to activate 8 workers on that queue. I was expecting that Laravel will know NOT to run the same job twice but I was surprised to discover that it did. 
  Same job was taken cared of by more than one worker and therefore weird stuff started to happen.</p>
  
  <p>The thing is that one year ago I wrote the same mechanism for another Laravel project (but on Laravel version 5.1) and the whole thing worked out of the box. I didn't have to configure anything.</p>
  
  <p>Anyone can help?
  Thank you.</p>