update Mathjax to v4

[bradybus]

markdown-viewer/build/mathjax/package.json

Line 7 in ccf738f

"mathjax": "3.2.2"

I was adding the "new" (as of 2022) mathtools symbols to my markdown cheatsheet, but found they would not render. Mathjax just added support for these new symbols in version 4.0, released in August.

Here is the main docs page for migrating v3 to v4:

https://docs.mathjax.org/en/stable/upgrading/v3.html