Replace faulty colon with a semi-colon

Closes https://github.com/simplesamlphp/simplesamlphp/issues/962

lib/SimpleSAML/IdP.php

@@ -485,7 +485,7 @@ class IdP
         if ($assocId !== null) {
             $this->terminateAssociation($assocId);
             $session = Session::getSessionFromRequest();
-            $session->deleteData('core:idp-ssotime', $this->id.':'.$state['saml:SPEntityId']);
+            $session->deleteData('core:idp-ssotime', $this->id.';'.$state['saml:SPEntityId']);
         }
 
         // terminate the local session