Use $STACK to detect stack
Use $STACK to detect stack

crigor/buildpack-elixir-mix-env,gogolok/cloudfoundry-buildpack-elixir,hectorip/buildpack-elixir-phoenix,cloud8421/heroku-buildpack-elixir,camshaft/heroku-buildpack-elixir,bbhoss/cloudfoundry-buildpack-elixir,aerosol/heroku-buildpack-elixir,HashNuke/heroku-buildpack-elixir,teodor-pripoae/heroku-buildpack-elixir,yuku-t/heroku-buildpack-elixir,fcruxen/heroku-buildpack-elixir,danielberkompas/heroku-buildpack-elixir,lbarratt/heroku-buildpack-elixir