npm: Migrate to package-lock.json v2 schema.

This is an automated action by the NPM CLI which migrates from the v1
spec used by NPM versions 5 and 6, to v2, which is a migratory spec used
by NPM v7 (and is still readable by NPM v5/v6) [^1].

Given that NPM v6 shipped with NodeJS v14, which goes fully EOL at the
end of April [^2], and given that NPM is mostly an evergreen-release
project that provides best-effort-basis security-only backports to NPM
versions that shipped with a maintained version of NodeJS [^3], we can
expect to be free to upgrade to the v3 package-lock.json schema this
upcoming summer or later.

[^1]: https://docs.npmjs.com/cli/v9/configuring-npm/package-lock-json#lockfileversion
[^2]: https://github.com/nodejs/release#release-schedule
[^3]: https://github.com/npm/cli/wiki/Support-Policy

Author: klardotsh