[FEATURE] update node-gyp to 5.1 at the very least

[Pomax]

As Python 2.7 was finally abandoned on January 1st of this year and should no longer be a prerequisite for anything in the computing world (except maybe folks on macos, all of whom should have python3 installed anyway now that 2.7 is dead) it would be a good idea to bump the version of node-gyp to 5.1.0 or higher (see nodejs/node-gyp#2052)

[Pomax]

Correction: a decisions was made late December of last year to push the date back to April first, 2020, so there's a few weeks left before Python 2.7 EOL yet. Of course, it would still be wise to uplift node-gyp before then.

[ljharb]

See #771, #287.

[Pomax]

perfect, closing as duplicate.

(hopefully the PRs won't go stale over travis not passing...)