Update composer.json, fixing license for packagist

composer.json

@@ -4,7 +4,7 @@
 	"description": "Mail Templating Service",
 	"homepage": "https://www.sgalinski.de",
 	"license": [
-		"GPL-2.0+"
+		"GPL-2.0-or-later"
 	],
 	"version": "4.3.3",
 	"repositories": [