Upgrade npm to 6.2.0 to fix Windows long file path issues

[daviwil]

Description of the Change

This change updates apm to use npm 6.2.0 to benefit from some major dependency restructuring and flattening that shaved about 60 characters off of npm's directory tree paths, specifically to aid with installing Node.js on Windows.

Since we've been fighting with "path too long" errors with Squirrel for a long time, this new version of npm is a welcome relief and a path forward to finally deliver side-by-side Atom release channel installations on Windows.

Alternate Designs

I also tried running npm dedupe in Atom's apm folder in various different ways and it either broke apm, broke Atom's app packaging, or had no real effect. Updating to npm 6.2.0 is the only thing that brought results.

I also tried updating to npm 6.3.0 but ran into some issues with apm after doing that, so it's probably better to hold off for now.

Benefits

• Shorter Atom installation paths on Windows
• One step closer to having side-by-side installation channels on Windows Multiple Atom release channels can't be installed side-by-side on Windows atom#9247

Possible Drawbacks

Minor bugs introduced by 6.2? So far everything seems solid.

Applicable Issues

• Multiple Atom release channels can't be installed side-by-side on Windows atom#9247

[smashwilson]

👍

I also tried updating to npm 6.3.0 but ran into some issues with apm after doing that, so it's probably better to hold off for now.

Can you open an issue with some details about that one? I'd rather not get stuck being too far behind again...

[daviwil]

Yeah I'll see if I can track down exactly what the issue was and then file an issue.