Use SPDX 3.0 license identifier

SPDX released version 3 of their license list (<https://spdx.org/licenses/>),
which changed the FSF licenses to explicitly end in -only or -or-later
instead of relying on an easy to miss + symbol.

Bug: T183858
Change-Id: Id75a37eab27282ca7797fa3e6ceb92750c59477f

composer.json

@@ -10,7 +10,7 @@
 	],
 	"homepage": "https://www.mediawiki.org/wiki/Extension:UniversalLanguageSelector",
 	"license": [
-		"GPL-2.0+",
+		"GPL-2.0-or-later",
 		"MIT"
 	],
 	"support": {