add a fitbit compliance fix

[brad]

This adds a compliance fix for the Fitbit API so that errors that occur during access token or refresh token fetching get properly surfaced.
https://dev.fitbit.com/docs/oauth2/#authorization-errors

We have been using this successfully with the python-fitbit library for a few weeks now: https://github.com/orcasgit/python-fitbit/blob/master/fitbit/compliance.py

[coveralls]

Coverage decreased (-0.06%) to 86.696% when pulling cfc5af9 on orcasgit:fitbit-compliance into 476ba75 on requests:master.

[coveralls]

Coverage decreased (-0.06%) to 86.696% when pulling 3b37810 on orcasgit:fitbit-compliance into 476ba75 on requests:master.

[coveralls]

Coverage decreased (-0.06%) to 86.696% when pulling 3b37810 on orcasgit:fitbit-compliance into 476ba75 on requests:master.

[coveralls]

Coverage decreased (-0.06%) to 86.696% when pulling 3b37810 on orcasgit:fitbit-compliance into 476ba75 on requests:master.

[Lukasa]

This seems reasonable to me, thanks @brad! ✨

[brad]

Thanks @Lukasa!