Stealing the cached-bundle and s3-put scripts from hub

http://mislav.uniqpath.com/2013/12/travis-cached-bundle/
Use a different bucket
Move release dependency to script/release
Use RVM in Go build
Bump Rake
Add TRAVIS_RUBY_VERSION since it's not available in the go build
Merge pull request #153 from jingweno/bundler_cache

Speeding up Travis CI builds by caching gems