Upgrading Netty version from 3.4.2 to 3.5.1 to attempt to fix the H13 re...

...sponses we've been getting on Heroku perhaps related to http://play.lighthouseapp.com/projects/57987/tickets/1708-new-more-secure-cookie-encoding-triggers-a-bug-in-netty-342-and-results-in-dropped-connections