Correct name of CC BY-SA 4.0 license

Version 4.0 of the CC BY-SA license was written in a way that didn't
require to be ported to different legal jurisidictions, thus it is
correctly known as the "Creative Commons Attribution-ShareAlike 4.0
International License" not the "Creative Commons
Attribution-ShareAlike 4.0 Unported License".

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>