adds colors to support gitlens hover

[aharvard]

Hey, @wesbos — Happy hacktoberfest to you good sir!

This PR addresses issue #185 reported by @kingcard1131.

Here is a before and after:

I discovered these new token scopes by digging thru https://github.com/primer/github-vscode-theme/blob/a9acf82f22bf810baf445b6efe5689aa89b4949c/src/theme.js#L487-L508... very informative. Also they have a really sweet theming setup over there 😻 if you've not seen it, check it out.

Thanks for considering!

[Sanqui]

This looks great, any chance we could get it merged (even if it's not October)?

[wesbos]

Sorry this took so long - good change!