[TASK] Configure Travis for better build performance
* set sudo: false so Travis can use their new container-based infrastructure
* enable bundler caching
* Also remove the commented-out rvm 1.9.2 from .travis.yml as this version
  has reached its end of life some time ago.
Merge pull request #262 from braingourmets/task/travis-performance

[TASK] Configure Travis for better build performance