* datefudge: work correctly even if GNU date is not in PATH
Examples in manual assumes advanced features from date(1) like "last
Friday", which only available in GNU coreutils version of date(1)
utility. Without this patch, most examples from datefudge(1) manual will
fail in busybox environment, which is confusing.
* Apply suggestions from code review
* Update pkgs/tools/system/datefudge/default.nix
Co-authored-by: Sandro <sandro.jaeckel@gmail.com>