Change .env to .env.production

:fork_and_knife: In service to https://github.com/opscode/supermarket/pull/399 this changes the .env template to be .env.production as we're now taking advantage of dotenvs environment features. .env.production will take precedence over .env.
Awesome thanks for the heads up, I'm not super familiar with serverspec yet. I amended my last commit to use serverspec's file resource.