Update html5shim/shiv to 3.6.1, use a CDN

This commit:
 - Switches html5shiv to a CloudFlare cdnjs (from Google Code)
   [Google Code sets a Cache-Control max-age of 3 minutes :( ]
 - Makes html5shiv protocol-relative (not sure where Issue #1706 went)
 - Updates html5shiv from vpre3.6 to 3.6.1 which fixes a few minor bugs

New html5shiv home: https://github.com/aFarkas/html5shiv

Signed-off-by: Nick Semenkovich <semenko@alum.mit.edu>