Turn on SSL in production. Closes #41.

Heroku apps are SSL-enabled by default, and to take advantage of that, all we need to do is turn on SSL in the Rails production config file.

To use SSL with a custom domain, read the following section in the Wiki:

https://github.com/codeforamerica/ohana-api/wiki/How-to-deploy-the-Ohana-API-to-your-Heroku-account#using-a-custom-domain-name-and-ssl-configuration