Use travis-ci.org for ruby project in subdirectory

Put something like this in your .travis.yml

language: ruby
rvm:
 - "1.8.7"
 - "1.9.2"
 - "1.9.3"
 - jruby-18mode
 - jruby-19mode
 - rbx-18mode
 - rbx-19mode
gemfile: SUBDIRECTORY/Gemfile
script: sh -c 'cd SUBDIRECTORY && bundle exec rake'