package/s6-rc: bump to version 0.5.2.1

Update license hash due to year change.

http://skarnet.org/cgi-bin/archive.cgi?1:mss:1515:mhcdpginfgieagphalne



Signed-off-by: Dick Olsson <hi@senzilla.io>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>