.travis.yml: change ruby versions for tar and gem integration tests

 * In tar and gem integration tests, Ruby versions are changed to
   MRI 2.0.0 and jruby-19mode.
 * Add jruby-18mode
 * Add rbx-2.1.1
.travis.yml: rbx version is changed to 2.2.3

 * rbx version is changed to 2.2.3
 * add dependent gems for rbx platforms, described in
   http://docs.travis-ci.com/user/languages/ruby/
.travis.yml: workaround to avoid error in Ruby 1.8.7 and jruby-18mode

 * workaround to avoid error in Ruby 1.8.7 and jruby-18mode
   (reference: https://github.com/rubygems/rubygems/pull/763 )
Ruby 2.1 workaround: Array#uniq does not always choose the first item

 * Ruby 2.1 workaround: Array#uniq does not always choose the first item.
   Thanks to Andrew Grimm who reported the issue.
   (https://github.com/bioruby/bioruby/issues/92 )
   Note that the behavior change is also regarded as a bug in Ruby and
   is fixed. (https://bugs.ruby-lang.org/issues/9340 )
.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