qt5 - MathJax not used in generated Sphinx docs

[tcbennun]

Generating the docs in the ESS_GUI branch results in pages that look similar to master, but the MathJax? script is never included in the HTML file despite the Sphinx configuration being seemingly identical between master and ESS_GUI.

In the HTML source, equations are still within <span class="math"> tags as usual. They just aren't rendered, e.g.

It's worth noting that the conda environment YAML file in ESS_GUI doesn't specify Sphinx, so I'm using sphinx=1.5.1=py36_0 since that's the earliest Sphinx version supporting Python 3.6. In master, we still use sphinx=1.4.8=py27_0. Sphinx's own documentation on MathJax? did not change between 1.4.8 and 1.5.1.