Replace date.js lib with patched version.

date.js was redefining Date.now() to return new Date()
(object) instead of current timestamp (number).  This broke
other javascript (e.g. d3js) due to changing the browser API
behaviour.

It looks like date.js is not maintained but cloudflare
hosts a version that is patched to remove the issue.

http://cdnjs.cloudflare.com/ajax/libs/datejs/1.0/date.min.js