MathJax doesn't work because it's loaded via http

[followup for BCLOUD-5420. Thanks for the willingness to support math!]

I've created a repo to test the restructuredtext math support:
https://bitbucket.org/cbensf/test-math/\\
docutils marks inline and display math with class="math but they're not rendered,
at least in Chrome. Console says:

[blocked] The page at https://bitbucket.org/cbensf/test-math/ ran insecure content from http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-MML-AM_HTMLorMML.\\
[blocked] The page at https://bitbucket.org/cbensf/test-math/ ran insecure content from http://cdn.mathjax.org/mathjax/latest/config/TeX-MML-AM_HTMLorMML.js. ...and so on...

Accessing bitbucket via http redirects to https, so can't even try that.

=> You need to use HTTPS address of mathjax CDN: http://www.mathjax.org/resources/faqs/#problem-https

According to http://docutils.sourceforge.net/docs/user/config.html#math-output\\
this can be configured as:

[html4css1 writer]
math-output: MathJax https://c328740.ssl.cf1.rackcdn.com/mathjax/latest/MathJax.js?config=TeX-MML-AM_HTMLorMML

(the url while ugly is "stable and safe to use" — see mathjax FAQ above)