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.

heroku/heroku-buildpack-nodejs,caiorogerio/heroku-buildpack-grunt,heroku/heroku-buildpack-nodejs,Scalingo/nodejs-buildpack,heroku/heroku-buildpack-nodejs,heroku/heroku-buildpack-nodejs,caiorogerio/heroku-buildpack-grunt,apiaryio/heroku-buildpack-nodejs-grunt,heroku/heroku-buildpack-nodejs,caiorogerio/heroku-buildpack-grunt,Scalingo/nodejs-buildpack,Scalingo/nodejs-buildpack,Scalingo/nodejs-buildpack,Scalingo/nodejs-buildpack