Won't install with Node version above 8.14

[CH-Chonsu]

Hi! :)

We're using markdown-document and are fairly happy with it. But since we're now using a Node Version above 8.14 npm/yarn won't let us install your package anymore. We'd be glad if you could provide us a fix.

• Thank you a lot in advance.

Kind regards from the HoracePGreeley Fanclub
C.

[marcel-hofer]

This may have been a problem with the wkhtmltopdf library and how its installation worked.
I updated this library to the latest version and published v0.2.1 of the package.

I was able to sucessfully test the installation of the new package and the generation of a simple test document under node v12.2.0 and npm v6.9.0.

This version also includes a fix for #20, which was reported by our friend HoracePGreeley a long time ago.