Confirm that all relevant labs have been converted from "old" `bats` to `bats-core`

[NicMcPhee]

It looks like the original bats project has been abandoned, the currently active one is bats-core. (See, for example, the bats-core README and this issue on the original bats repo.

Given this, we should probably move the lab over from bats to bats-core, and make any necessary updates to these Practicum labs.

I think I did this for most/all of the relevant labs for F20, but I should go through and confirm that.