GUACAMOLE-362: Add missing parameter documentation for credentials object.

extensions/guacamole-auth-cas/src/main/java/org/apache/guacamole/auth/cas/ticket/TicketValidationService.java

@@ -63,6 +63,9 @@ public class TicketValidationService {
      *
      * @param ticket
      *     The ID ticket to validate and parse.
+     * @param credentials
+     *     The Credentials object to store retrieved username and
+     *     password values in.
      *
      * @return
      *     The username derived from the ticket.