* gnu/packages/python.scm (snakemake): Update to 4.2.0.
[propagated-inputs]: Add python-appdirs, python-configargparse, python-pyyaml,
and python-ratelimiter, which are dependencies as of Snakemake 4.1.0.
Signed-off-by: Marius Bakke <mbakke@fastmail.com>