Bump xml-common

Author: tvdijen

composer.json

@@ -15,7 +15,7 @@
 
         "simplesamlphp/assert": "~2.0",
         "simplesamlphp/saml2": "~6.1",
-        "simplesamlphp/xml-common": "~2.7",
+        "simplesamlphp/xml-common": "~2.8",
         "simplesamlphp/xml-security": "~2.3",
         "simplesamlphp/xml-ws-addressing": "~1.3",
         "simplesamlphp/xml-ws-security-policy": "~1.2",