Hello, all. I would like to contribute this tweak that I have been using in my personal config (though in the form of advice).
As with Python, in Ruby there is significant need to be able to specify the Ruby command invoked. For instance when managing dependencies with Bundler (which is very common), in order to resolve imports you need to run `bundle exec ruby` instead of just `ruby`. This patch allows specifying the Ruby command in the same vein as ob-python's :python header arg. This is my first contribution to org-mode, so please let me know if I have missed anything. Thanks, Aaron
