icon: update mentioned license of the hand from human-icon-theme

See
http://bazaar.launchpad.net/~ubuntu-art-pkg/human-icon-theme/ubuntu/revision/103
for the upstream commit:
'Update COPYING to CC-BY-SA 3.0, as declared and intended in
debian/copyright.'

COPYING

@@ -37,5 +37,5 @@ The hand is from Ubuntu's human-icon-theme, which is CC by-sa
 (c) Jeff Waugh <[email protected]>
 (c) Daniel Holbach <[email protected]>
 (c) Martin Pitt <[email protected]>
-Creative Commons Attribution-ShareAlike 2.5 License Agreement
-http://creativecommons.org/licenses/by-sa/2.5/
+Creative Commons Attribution-ShareAlike 3.0 License Agreement
+http://creativecommons.org/licenses/by-sa/3.0/