We now support the 'Dr' title on order creation

The list of supported passenger titles on order creation has been updated to include Dr on Duffel.

While the majority of airlines support this title, there are a few (Easyjet, Spirit, Transavia and Volaris) that will continue to return an invalid_passenger_title error as we roll out coverage of the Dr title.

Our documentation and dashboard have been updated to reflect this and API users should no longer receive validation errors when submitting passengers with a Dr title for the airlines that support it.