Upgrade to react-markdown 7?

[akx]

Hey there!

It looks like this package is using a pretty old version of react-markdown and could probably, with some elbow grease, be upgraded to v7. I noticed this via a dependabot warning on trim@0.0.1 via @nteract/markdown#react-markdown#remark-parse#trim.

Doing that would also allow using https://github.com/remarkjs/remark-math which seems to, according to some Git history sleuthing – nteract/nteract@61fa1a4, be the evolution of this repo's remark-math stuff. That might help with #5.

I could (try to) do the work, unless there's a good reason not to? :)

[captainsafia]

@akx Contribution is always welcome! As always, the lag with upgrades sometimes is the time needed to do the upgrade and all the follow ups that come with. Help is definitely appreciated.