License string corrected

Correct license abreviation is CC BY-SA 3.0.
(per https://creativecommons.org/licenses/by-sa/3.0/)
Affects:
* license-footer-name

Spotted by Jopparn at https://translatewiki.net/wiki/Thread:Support/About_Wikimedia:Wikipedia-ios-license-footer-name/sv

Change-Id: Icaa1afa24e53d75af195ed332b14111f4e40e19b