update tap tests to hit no external dependencies.
test: Add test to verify npm-registry-mock version

I keep getting myself into weird cases where I have an outdated copy of
npm-registry-mock, and so tests fail, and I spend several minutes digging
only to find that it's because I didn't update after the package.json dep
changed.

Add a test to alert to this situation, which will run BEFORE all the other
tests start failing horribly.