Update mathjax default in revealjs

[olivroy]

Description

In RStudio / rmarkdown, the default mathjax was updated to 2.7.9 recently. I thought it may be good to do the same in Quarto. Simply changing this line would probably do the trick?

quarto-cli/src/format/reveal/format-reveal.ts

Line 90 in 6b363d9

"https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.0/MathJax.js?config=TeX-AMS_HTML-full",

[cscheid]

Seems reasonable to me. I created an issue to track, though @cderv is the expert on our revealjs subsystem and it's his call to make.