Don't publish tests to npm

When publishing to npm, it's unnecessary to publish all 19 MB of test files.

Sure, tests are nice, but when installing a library I don't expect to run all tests on it. If I discover a bug in it, I clone it from the repo, and run the tests there.

Having to download almost 20 megs of stuff I will never use seems a bit excessive.

Comparatively, the footprint in my node_modules for express is around 640k.