Fix 'license-name' to match SPDX conventions

References:
http://spdx.org/licenses/
https://www.mediawiki.org/wiki/Manual:$wgExtensionCredits#license-name

While 'GPLv2' could mean 'GPLv2 only', the comment at the top of
the file clearly states 'GNU General Public License 2.0 or later'.

Change-Id: I1546f4caef78a17f945c903f2f28d53bf830ca95

Cite.php

@@ -30,7 +30,7 @@ $wgExtensionCredits['parserhook'][] = array(
 		'Steve Sanbeg'
 	),
 	'descriptionmsg' => 'cite-desc',
-	'license-name' => 'GPLv2',
+	'license-name' => 'GPL-2.0+',
 	'url' => 'https://www.mediawiki.org/wiki/Extension:Cite'
 );