Triage Travis CI configuration

  * Use latest rubies for travis
  * Switch to travis-handled rbx version; add dependent gems
  * Use latest appraisal gem that supports Bundler platforms
  * Update appraisal gemfiles to use latest appraisal
  * Add fragile rubies to allowable failures in travis-ci
Merge pull request #45 from scudco/triage-travis-ci

Triage Travis CI configuration