Escape backslashes so that they make it to MathJax

[moble]

Without the escapes, the LaTeX doesn't render properly, as can be seen by following the link to codepen from the docs.

[moble]

Bump. Here's a codepen test of the corrected code showing that it does actually work, unlike what's in the manual currently.

@red-patience

[moble]

Bump. Tiny PR to make the math render correctly.