Fix for bug in IronMQ integration

The current getQueue function doesn't return the queue name when new messages are pulled from IronMQ.

```
public function getQueue()
{
    return array_get(json_decode($this->job->body, true), 'queue');
}
```
I'm not sure if this was caused by an API change by Iron.io or a change to the IronMQ repo but the queue name is no longer attached to the job->body. These changes push the queue name onto the job once it's returned from IronMQ which is then passed on to the IronJob class.