CI: Update RTD configuration file

RTD has finished their switch to 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: Id0f2149b2552c7bad571acfb82d2f8827495341c
Signed-off-by: Anil Belur <abelur@linuxfoundation.org>
2 files changed