Remove thin implied dependency

Apparently between 0.9.0 and 0.9.0.1.wp an explicit dependency on thin (an event machine-based web server) was introduced.  I think it's due to the fact that our fork of their code adds it as a development dependency (here), but the general lib/thrift.rb requires thrift/server/thin_http_server no matter what (here), which, in turn, requires thin.   This causes all things that reference thrift, even if they don't care about the web server, to explicitly require the thin gem.  

Could you look over this pull request which removes that and if you agree, commit and publish a new gem version?