package/gnuchess: bump to version 6.3.0

Release notes:
https://cgit.git.savannah.gnu.org/cgit/chess.git/tree/ChangeLog?h=v6.3.0



Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
[Julien: add tag in release note URL]
Signed-off-by: Julien Olivain <ju.o@free.fr>