Converted one test to testify for grins.

I like it more. I shall switch over stuff as I work on it.
Add heroku command with semi-useless implementation.

It only spits out the command it would otherwise run, but I ran into
some issues shelling out and I want to make a separate commit out of
that. I suppose you could run it in backticks in the shell now and get
minor use out of it.
Replace some code with a stdlib function I found.
Convert actions/heroku to testify.

I will be needing mocks in a moment.