CI Updates

[joaocgreis]

@nodejs/node-gyp FYI, let me know if there's an issue with any of this.

In nodegyp-test-pull-request:

• Updated Node.js and npm versions.
• Changed PR_ID to REMOTE_REF, this allows us to test anything invoking the multiple subjobs at once. The job name remains "test pull request", so the whole job tree could probably be reorganized to make more sense. For now, we can think of it as "not exclusively".
• Skip Node.js v4 for node-gyp v4 (v0.10 and v0.12 were aready skipped).

In nodegyp-test-commit:

• Updated to use https://github.com/npm/cli instead of https://github.com/npm/npm (apparently, all the old releases are there).

[joaocgreis]

CI is currently broken for master, PR to fix: #1561

[joaocgreis]

Added v11.0.0 to the matrix. Also added v6.0.0 because that's the oldest we support for v4, so should be tested.

[joaocgreis]

Had to change to v6.2.1 because NVS was having issues with 6.0.0 - probably because the zip/7z packages are not available.

[refack]

NVS was having issues with 6.0.0

But besides that it's a great tool for this task, right?

[joaocgreis]

Haven't reviewed it carefully but it looks great 👍