updated readme to reference travis-ci.org instead of the heroku url
updated readme to reference travis-ci.org instead of the heroku url

flores/travis-ci,flores/travis-ci,fxposter/travis-ci,openeducation/travis-ci,flores/travis-ci,openeducation/travis-ci,fxposter/travis-ci,fxposter/travis-ci,openeducation/travis-ci