deps: upgrade npm to 3.9.3

Checklist

• tests and code linting passes
• a test and/or benchmark is included
• documentation is changed or added
• the commit message follows commit guidelines

Affected core subsystem(s)

deps

Description of change

Hey all! This release includes 4 releases of npm. Some notable changes:

• npm/npm@42d71be npm/npm#12685 When using npm ls <pkg> without a semver specifier, npm ls would skip any packages in your tree that matched by name, but had a prerelease version in their package.json. (@zkat)
• npm/npm@f04e05 npm/npm#10013 read-package-tree@5.1.4: Fixes an issue where npm install would fail if your node_modules was symlinked. (@iarna)
• b894413 #12372 Changing a nested dependency in an npm-shrinkwrap.json and then running npm install would not get up the updated package. This corrects that. (@misterbyrne)
• This release includes npm@3.9.0, which is the result of our Windows testing push -- the test suite (should) pass on Windows now. We're working on getting AppVeyor to a place where we can just rely on it like Travis.

Changelogs

• v3.9.0
• v3.9.1
• v3.9.2
• v3.9.3

r: @iarna r: @TheAlphaNerd r: @Fishrock123