[Feature Request] Update to Katex 0.12.0

Today I tried to used make a Joplin note containing some bra-ket notation in Katex, as shown here in the Katex documentation, and Joplin was not able to handle the \ket in my Katex block. It looks like support for that notation was only added in Katex 0.12.0 since I don’t see any mention of bra-ket notation in the documentation of the previous version Katex 0.11.1. Joplin’s package.json files all specify version “^0.11.1” for Katex – can we update that to Katex 0.12.0?

I updated the package.json files to use Katex 0.12.0 on a local fork of Joplin and confirmed that with 0.12.0 I can use bra-ket notation, which I’m really excited about. I was going to make a Pull Request but saw the recommendation in CONTRIBUTING.md to bring up changes on the discourse first. Any thoughts on this change? I’m ready to go with the Pull Request if this is a welcome change.

Thanks! I really enjoy using Joplin and would be exciting to make a small contribution to the code!