CNAME file is blown away on every deploy

[myronmarston]

It took me a while to figure out why our CNAME file wasn't working. We had it in our source branch ut not in our master branch. As github's docs state, it needs to be in the master branch:

https://help.github.com/articles/adding-a-cname-file-to-your-repository/

I added it to master and that made it work. Then I noticed on the next deploy that it was blown away by the deploy (since middleman apparently force pushes -- is that really necessary?).

@JonRowe / @mootpointer -- do either of you know how to configure our deploy so that it won't blow away extra files (such as the CNAME) on each deploy? For now I'm just re-adding it manually after each deploy but that's no fun.