improve documentation at getJobs()

[shmulikmak]

at https://github.com/OptimalBits/bull/blob/develop/REFERENCE.md#queuegetjobs the first parameter is "types", I think you should follow the convention and call it a STATE as you call it in other function like getState etc..

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.