Address githubs' new access token format

[inaimathi]

• As per https://developer.github.com/changes/2020-02-10-deprecating-auth-through-query-param/ we now need to send the access token as part of the Authorization header.

This commits sends both, because I'm not sure how widespread the change is, and still want this client to be compatible with OAuth providers other than github. Maybe a config option that defaults to header for github would be a better option?