suggestion: check NPM version

[electronstudio]

Debian's NPM is out of date and I had to upgrade it as suggested in the docs before package upload would work. The error wasn't obvious ("missing package.json") so maybe you could do a check of the NPM version and tell the user to upgrade if necessary.

[shannah]

Thanks for the suggestion. You're right. That error message doesn't look very helpful. I'm not sure what the actual minimum npm version is, so I'll pick the version I'm using, I guess, and add a check to make sure that it is running at least that version.