modify for ruby 1.8 support

I guess I have the personality that makes it easier to port the code than to use ruby 1.9, I have a patch that 
* changes all the -> to lambda
* requires rubygems to pull in the json lib, if it's installed through "gem install json"

Given that the default ruby on Mountain Lion is still 1.8, I think this is worth merging in.

I'm not terribly happy about having to pull in rubygems, but I couldn't see a way around it