Make this package installable with npm

[davidmehren]

Hi!

A fork of this package was available via npm for a long time and has now been unpublished. This breaks builds for many projects, see for example hedgedoc/hedgedoc#39

Could you add the version key in your package.json so that this repository can be used as a dependency in projects which use npm (see https://docs.npmjs.com/files/package.json#git-urls-as-dependencies)?

[ccoenen]

I would love this, too! this way, you wouldn't even have to publish to npm if you don't want to.