p.Tune is only for cutting down pool size, but not support enlarge.

Created by: laodano1

In the Tune Method, the scale up the pool size should be supported also. So, before do the pool size change, check which one is bigger for the p.Running() and size, the using the bigger one to minus the small one, then assign the result to diff. What do you think?

func (p *Pool) Tune(size uint) ... ### diff := p.Running() - int(size) for i := 0; i < diff; i++ { p.retrieveWorker().task <- nil }