Update Bootstrap version in MVC sample layout page

This PR updates @Bootstrap framework version used in MVC sample layout page to latest version as of time of this PR.
http://blog.getbootstrap.com/2014/11/12/bootstrap-3-3-1-released/
https://github.com/twbs/bootstrap/releases/tag/v3.3.1

The update is transparent to project source as implementation uses CDN resource - so no other files are affected by this PR.