.travis.yml: fix mistakes
gemfiles/Gemfile.travis-rbx: Gemfile for rbx (Rubinius) on Travis-ci

 * gemfiles/Gemfile.travis-rbx: Gemfile for rbx (Rubinius) on Travis-ci
 * .travis.yml is modified to use gemfile/Gemfile.travis-rbx for rbx.
suppress "source :rubygems is deprecated" warning