Validate license type?

[pdehaan]

There are a few new license changes in newer versions of npm.

https://docs.npmjs.com/files/package.json#license
http://npm1k.org/

See https://www.npmjs.com/package/spdx

[Kikobeats]

sounds good, but I feel that finepack is oriented with whatever json file, not only npm package files, and this field maybe is too specific. If you can use spdx for check the license, why not use it?