Fixed documentation for Queue clean call to match code expectation

Created by: alecl

README.md waiting -> wait

code reference: https://github.com/OptimalBits/bull/blob/master/lib/queue.js#L913

Also, there are places in the documentation where words like 'paused' (queue count) or 'stalled' (queue event) are used but those can't be cleaned? I thought a queue gets paused not a job. Thanks for any clarification.