[TASK] Configure Travis CI for better build performance
[TASK] Configure Travis CI for better build performance

* set sudo: false to allow Travis to use the container-based infrastructure
* enable bundler caching

sideci-sample/sideci-sample-rails_best_practices,beanieboi/rails_best_practices,flyerhzm/rails_best_practices,andela-iokonkwo/rails_best_practices,railsbp/rails_best_practices,flyerhzm/rails_best_practices,beanieboi/rails_best_practices,railsbp/rails_best_practices,neomadara/rails_best_practices,beanieboi/rails_best_practices,andela-iokonkwo/rails_best_practices,sideci-sample/sideci-sample-rails_best_practices,neomadara/rails_best_practices,railsbp/rails_best_practices,andela-iokonkwo/rails_best_practices,neomadara/rails_best_practices