Update saml2

Allow the new major version to be used as well (lock-file remains at 3.x)

composer.json

@@ -45,7 +45,7 @@
         "gettext/gettext": "^4.6",
         "phpmailer/phpmailer": "^6.0",
         "robrichards/xmlseclibs": "^3.0",
-        "simplesamlphp/saml2": "^3.3",
+        "simplesamlphp/saml2": "^3.4 || ^4.0",
         "simplesamlphp/simplesamlphp-module-adfs": "^0.9",
         "simplesamlphp/simplesamlphp-module-authcrypt": "^0.9",
         "simplesamlphp/simplesamlphp-module-authfacebook": "^0.9",