git-bats-demo solution, part 6 of 6 (cleaning up shellcheck)

This is now the 6th of 5 videos (!), where I return to this problem after several years and use the `shellcheck` tool to highlight a few key style/safety weak spots in my solution. In this video I use `shellcheck` to find these issues, explain them, and fix them.

Some useful resources for best practices of `bash` scripting:
* I didn't use that here, but it's worth knowing about.

These videos assume that you know the basics of command line interaction (`ls`, `cd`, `rm`, etc.). if you're playing along at home you should definitely feel free to pause anytime I do something that appears mysterious and do a little searching for additional information.

[funfunfun]

Thanks Nic, this series was super helpful. We are moving more to developing tools and steps in our CI/CD in shell scripts. I now have the confidence to back them with automated tests