[FEATURE]: Update library to handle MathJax v4 and remove v2 support

[camdecoster]

Description

Update library to handle MathJax v4 and remove v2 support.

Why should this feature be added?

• v4 was recently released and mostly adds features which could be useful to users
• v2 contains a security vulnerability (ReDoS attack). While this issue doesn't affect the library much (only used as a dev dependency), it shows up as a warning with npm audit.
• The latest v2 release came out in 2020
• Removing v2 support would simplify the code

Notes

• This would be a breaking change
• The upgrade process looks pretty straightforward
• Jupyter bundles a version of MathJax and the library needs to remain compatible with that