tidy up packaging

[shiftkey]

The current master branch generates a package that looks like this:

npm notice === Tarball Details ===
npm notice name:          registry-js
npm notice version:       1.0.7
npm notice filename:      registry-js-1.0.7.tgz
npm notice package size:  954.5 kB
npm notice unpacked size: 4.3 MB
npm notice shasum:        1d857d4d984856cfe96a6484dc56648059b8477e
npm notice integrity:     sha512-yiXLlt5AeZGOz[...]HYsiNUjWQufKg==
npm notice total files:   25

With this PR, we get it back down to something more sane:

npm notice === Tarball Details ===
npm notice name:          registry-js
npm notice version:       1.0.7
npm notice filename:      registry-js-1.0.7.tgz
npm notice package size:  23.6 kB
npm notice unpacked size: 74.4 kB
npm notice shasum:        ba7aa39fd04d72a59ce458006615f8dfc5d45a2a
npm notice integrity:     sha512-m3PYW1jZGwWTs[...]sani+PeeAIG/Q==
npm notice total files:   21