Publish latest version to npm

Could you publish the latest version? This currently published version from 11 months ago breaks when using more than 2 caveats and this PR fixed it: cbd8795

For those that get the Invalid typed array length, just run npm install go-macaroon/js-macaroon#master to get the latest instead of 3.0.4

[jungleBadger]

@rogpeppe any chance to give this a look?