Add CNAME setup for apiumbrella.io domain.
Add CNAME setup for apiumbrella.io domain.

This pulls in the CNAME file from
https://github.com/NREL/api-umbrella/pull/114 so that it lives on the
master branch so it is part of the middleman build.

NREL/api-umbrella,NREL/api-umbrella,apinf/api-umbrella,apinf/api-umbrella,apinf/api-umbrella,NREL/api-umbrella,apinf/api-umbrella,NREL/api-umbrella,apinf/api-umbrella