Add missing use-statement

Author: tvdijen

src/Controller/AttributeServer.php

@@ -9,6 +9,7 @@
 use SimpleSAML\{Configuration, Error, Logger};
 use SimpleSAML\HTTP\RunnableResponse;
 use SimpleSAML\Metadata\MetaDataStorageHandler;
+use SimpleSAML\Module\saml\Message;;
 use SimpleSAML\SAML2\Binding;
 use SimpleSAML\SAML2\Binding\HTTPPost;
 use SimpleSAML\SAML2\Constants as C;