Errors returned by Nakadi don't have type field in Problem

[mdedetrich]

According to Nakadi's swagger (https://github.com/zalando/nakadi/blob/master/docs/_data/nakadi-event-bus-api.yaml#L2188-L2225), when Nakadi returns an error indicated by the Problem JSON type it should include the type field however the type field doesn't exist for a certain set of errors, i.e. 409 conflict when starting a Nakadi stream due to having no empty slots or cursor reset.