Dependency upgrades for mitigating a vulnerability

[KoenDG]

The codecov package had a vulnerability.

The istanbul package is no longer maintained. The project recommends switching to the nyc package, which was done.

The vulnerabilty, as per npm audit:

Severity: high
Command injection in codecov (npm package) - https://github.com/advisories/GHSA-xp63-6vf5-xf3v
codecov NPM module allows remote attackers to execute arbitrary commands - https://github.com/advisories/GHSA-5q88-cjfq-g2mh
Improper Neutralization of Special Elements in Output Used by a Downstream Component in Codecov - https://github.com/advisories/GHSA-mh2h-6j8q-x246
fix available via `npm audit fix --force`
Will install [email protected], which is a breaking change
node_modules/codecov

Tests ran, all passed locally.

[mathiasbynens]

Thanks!