Upgrade default setuptools to 5.4.1

Testing Done:
CI passed.  Looking at https://pypi.python.org/pypi/setuptools , there appear to be no expected breaking changes between our current setuptools (5.0) and this one.  We want this upgrade because of the bugfix in 5.1, and the other bug fixes since then seem good to pull in.

Reviewed at https://rbcommons.com/s/twitter/r/674/