package/swipl: bump version to 9.2.8
For change log since version 9.2.7, see:
https://www.swi-prolog.org/ChangeLog?branch=stable&from=9.2.7&to=9.2.8
Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>