Timers not always being cleared when closing, causes hanging process

Created by: jeffijoe

I'm run into a weird issue with closing the queue.

When calling queue.close(), it seems the timeout created by https://github.com/OptimalBits/bull/blob/master/lib/queue.js#L803 is not cleared (even though I can see in the code that it should be). I found this using wtfnode as my Jest process would not exit.

Commenting out line 803 that creates the timer makes it work as expected.

Additionally, doing

queue.close().then(() => queue._clearTimers())

also fixes the issue. Perhaps running it again at the end of close might be a good idea?