label as Ruby 1.9 (not 1.8) for rbenv
add remote gem source so `bundle install` will work

this is the error I got before this change:

$ bundle install
Your Gemfile has no remote sources. If you need gems that are not already on
your machine, add a line like this to your Gemfile:
    source 'https://rubygems.org'
Could not find PriorityQueue-0.1.2 in any of the sources