The Stasis Build Pack will run stasis to create and serve the site.
Add this language pack to your BUILDPACK_URL.
heroku config:add BUILDPACK_URL="https://github.com/markpundsack/heroku-buildpack-stasis.git"
Or, with a recent version of the heroku gem, set it at creation time:
heroku create --stack cedar --buildpack https://github.com/markpundsack/heroku-buildpack-stasis.git