Image quality and PNG images

[Atrejoe]

Great project, finally I have been able to render Html as images in a docker container.

One issue: image quality cannot be specified for PNG images, and doing will result in an error:

options.quality is unsupported for the png screenshots

In the code the image quality is always specified. see: https://github.com/bedrockio/export-html/blob/main/src/app.js#L58

This can be circumvented by using jpeg There also is a feature request asking for this misconfiguration not to return an error: https://github.com/puppeteer/puppeteer/issues/3460

I will play further with this. May specifying a url instead of the content would be nice too, but then we may be going into the realm of using puppeteer itself.