package/isl: switch to new site
isl.gforge.inria.fr no longer responds and the main site is now at
sourceforge.io. This change corresponds to the upstream commit that
updates the documentation [1].
[1] https://repo.or.cz/isl.git/commitdiff/002820d725479b456c97ca9b0d59d6b3e18f7ee4
Signed-off-by: John Keeping <john@metanate.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit 748b7878e90ab5813a6f48e156410cf38ef087d9)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
John Keeping