Thought I'd share what I did to get Nokogiri all working on my Yosemite set up.
gem install nokogiri -v '184.108.40.206' -- --use-system-libraries --with-xml2-include=/usr/include/libxml2 --with-xml2-lib=/usr/lib
gem install rdoc
bundle update libv8
This setup on mac will let me update tiny_tds. Still no luck with getting it to work on ubuntu.
Hopefully saved someone some time.