Travis CI currently broken

Due to a npm change, npm install modifies package-lock.json, which turns bots red (we check for modified files at the end of the script).

Blocking #892, #889, and any other PRs.

[nfischer]

@hbetts thanks for linking to the npm ticket. I figured this is probably intentional. The issue is that we need to conditionally run npm install for npm versions which don’t know about npm ci.

It would be nice to just install the newest npm and use that to install dependencies, but I think shelljs supports a wider range of node versions than npm.

One way to detect support (since I forget which version introduced it) would be:

$ npm help | egrep '\bci\b'

[nfischer]

#911 flakes as well, which makes me suspect ci-or-install works correctly (although is perhaps overly complicated), and it’s appveyor which causes the flakiness.