For discussion: proposed npm test to check jsonld

[nonword]

This PR proposes we add a node test suite to this repo so that we can test certain expectations about mapping documents before deploying. The proposed workflow would be:

• make changes to mappings locally
• run npm test
• if the tests succeed, everything we expect to be true about the mappings documents is verified, so we can safely deploy to master

Alternatively we could just connect Travis and catch errors after they're committed to master if testing locally is cumbersome.