language: bash
sudo: required
services:
  - docker
install: docker pull heroku/cedar:14
script: make test

language: bash
sudo: required
services:
  - docker
env:
  - STACK=heroku-16
  - STACK=cedar-14
install: docker pull "heroku/${STACK/-/:}"
script: make test-${STACK}

Test Heroku-16 and Cedar-14 in parallel on Travis
Test Heroku-16 and Cedar-14 in parallel on Travis

This reduces the wall-clock time from 16 minutes to 9 minutes.
