change CNAME URL because it's causing a build error

other branches have the CNAME file in them, and one of them has taken over the commonplacemagazine.org domain, resulting in the following GitHub error:

The page build failed with the following error:

CNAME already taken: commonplacemagazine.org

For information on troubleshooting Jekyll see https://help.github.com/articles/using-jekyll-with-pages#troubleshooting