Resolved Bundler issue

I was getting bundle: command not found, when I made a release to heroku. This suddenly popped up a few days back and I was able to resolve this by updating the bundler version to 1.3.2 from 1.2.1 in ruby.rb. Having spent a lot of time to figure out what the problem was, I feel this can go into the codebase as well. Thanks for the buildpack.