Updated gemspec to make sure it uses the right versions of Goliath & http_parser.rb

The current version of the code doesn't work with new versions of Goliath and http_parser.rb. I've updated the gemspec to make sure it installs the right versions of these gems.

Obviously the right thing to do will be to update the code to use the latest version of Goliath, but for now I figured this is better than nothing.