Add nyc support (istanbul is deprecated)

[k06a]

Going to upgrade?

warning solidity-coverage > istanbul@0.4.5: This module is no longer maintained, try this instead:
npm i nyc
Visit https://istanbul.js.org/integrations for other alternatives.

[cgewecke]

@k06a Maybe - there's kind of a big change between the istanbul and nyc output formats and the Istanbul API seems like it's worked quite well. Do you have a specific reason to prefer nyc?

I've been thinking that when I do this it will be an option.

[k06a]

@cgewecke I afraid istanbul may stop receiving updates, even with critical fixes.

[cgewecke]

@k06a I think that's true - it's archived. Also think it will remain stable for a long time - it does very basic stuff.

Was just looking at nyc and they don't really publish a programmatic API any more. Would probably just have to figure out how to pass the coverage.json file to the command line tool.

Have to look at the monorepo over there...

Am going to rename your issue and add it to the roadmap - thanks for opening this @k06a!

Interesting discussion about this at istanbuljs. The old API is heavily used by jest....

[cgewecke]

Small update: as an interim step, have forked istanbul and published our own copy as sc-istanbul so any dependency vulns etc can be addressed in this org if they arise. Left a few other notes about possible ways forward at #465.

This change will ship in 0.7.1