Fix div-by-zero error on zero input for LSS
Fix of "undefined method 'async' of nil class"

See https://github.com/JustinLove/autoscaler/issues/37 for details
QueueSystems#workers explicitely return number of engaged processes, using new SK3 API

Conflicts:
	CHANGELOG.md
LSS uses number of engaged workers as a minimum, to help avoid scaling down engaged workers

Conflicts:
	CHANGELOG.md