Updated the path element env var name

I'm not sure if this was a fluke or not, but it happened to me 3 times in a row: with `bin/setup` creating `env/OPENSHIFT_RUBY_PATH_ELEMENT` I was never able to start redis in a ruby-1.9 application.

I modified it to create `env/OPENSHIFT_REDIS_PATH_ELEMENT` instead, and now I can install and use Redis in a ruby-1.9 app.