Update Bootstrap latest to 3.3.1 version. Closes #2165

This is purely maintenance kind of PR.
Keeps version of Bootstrap used in JSBin in sync with latest 3.3.1
version.
http://blog.getbootstrap.com/2014/11/12/bootstrap-3-3-1-released/

Tests:
https://gist.github.com/peterblazejewicz/7e96aadf78f1ac47787d

Thanks!