Specify LGPL-2.1-or-later for packagist to stop complaining.

composer.json

@@ -4,7 +4,7 @@
     "type": "project",
     "keywords": [ "saml2", "shibboleth","oauth","ws-federation","sp","idp" ],
     "homepage": "http://simplesamlphp.org",
-    "license": "LGPL-2.1",
+    "license": "LGPL-2.1-or-later",
     "authors": [
         {
             "name": "Andreas Åkre Solberg",