CI: Update RTD configuration file

RTD has finished their switch requiring version 2 of their
configuration file and we must now update to work with it.

Ref:
https://blog.readthedocs.com/use-build-os-config/

Change-Id: I346da38afcad784832669dc1a38a577c249187fd
Signed-off-by: Anil Belur <abelur@linuxfoundation.org>
1 file changed