Switch to recommended Travis CI integration for appraisal
Switch to recommended Travis CI integration for appraisal

See https://github.com/thoughtbot/appraisal#travis-ci-integration

twalpole/compass-rails,electronicbites/compass-rails,amiuhle/compass-rails,chrise86/compass-rails,glebtv/compass-rails,Compass/compass-rails,ipmobiletech/compass-rails