Near as I can tell there is no -S option for rdoc, which is causing a warning on installation. So, it should either be updated or removed in the gemspec:

s.rdoc_options = '-SNw2', "-m#{readme_file}", '-t CodeRay Documentation'

While I'm here looking, this line is unnecessary since it's the default.

s.require_paths = ['lib']

Also, this could be removed:

s.rubyforge_project = s.name # It's dead, Jim

Update: looks like rubyforge_project was removed.