GUACAMOLE-1636: Fix a typo mistake `offscren`.
GUACAMOLE-1636: Fix a typo mistake `offscren`.

mike-jumper/incubator-guacamole-server,mike-jumper/incubator-guacamole-server,apache/guacamole-server,apache/guacamole-server,mike-jumper/incubator-guacamole-server,apache/guacamole-server,mike-jumper/incubator-guacamole-server