Remove instafail dependency

@jeffkreeftmeijer I saw this referenced in issues #29 and #20 so I thought I'd give you a bonus. :)

I didn't do any extensive testing and I _did_ leave the specs in a failing state (for shame!).  I basically just wanted to see if I could get it to work.

Everything appears to work just as if instafail was installed although I didn't do extensive testing. I just thought I'd put this out there.

Also, this is based on `update-ruby-progressbar-to-v1` so I'd either cherry pick these commits or merge that branch in first.