Return Promise from queue.start()

[MaksimLavrenyuk]

The solution to the problem https://github.com/jessetane/queue/issues/34

1) Change in logic. Previously, if you passed a callback to start, any error in the job interrupts the queue. Now the queue interrupts on error, regardless of callback in start. 2) Added Promise return from the start method.

[jessetane]

Will review as soon as I can, need a few more days, thanks

[jessetane]

thanks, sorry for the delay there