Replace deprecated default_config method
Replace deprecated default_config method

As of Lita 4.0, the default_config method is deprecated, and a warning
message is logged on launch.

Also define the previously undefined `auth` configuration item.

See http://docs.lita.io/releases/4/ under "Upgrading for plugin
developers" section on config for more.

daniely/lita-jenkins,miketheman/lita-jenkins,tuxmea/lita-jenkins