[AIRFLOW-XXX] Don't trust python-requests.org to run a valid HTTPS server (#6179)
[AIRFLOW-XXX] Don't trust python-requests.org to run a valid HTTPS server (#6179)

This is the 3rd or 4th time we've had a problem with the docs from
requests causing the docs step of our build to fail. So lets switch to
RTD.io instead as they are much better at this.

(cherry picked from commit 66a139d734bd434caa792007c3b980ca4cf8f931)

owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow