sysutils/s6-rc: Update to 0.4.1.0

Changelog:
http://git.skarnet.org/cgi-bin/cgit.cgi/s6-rc/plain/NEWS

While here:

• Set LICENSE_FILE.

PR: 232053
Submitted by: crest@rlwinm.de
Reported by: dewayne@heuristicsystems.com.au
Reviewed by: mat
Approved by: mat (mentor), maintainer timeout (moo@arthepsy.eu)
Differential Revision: https://reviews.freebsd.org/D17569