Support for Mapnik 3.0.22

[sommerluk]

Hi @nebulon42

Mapnik 3.0.22 has been released. Also mapnik-reference has been updated to 3.0.22. Furthermore a corresponding new npm package has been published with version number 8.10.0. You pointed out that his version number change requires a new CartoCSS release, but that this would not be much work. It would be great to have a new CartoCSS release, also for playing around with solutions for rendering of unpaved roads in openstreetmap-carto.

Also closes #496 ?

[nebulon42]

Done.

[sommerluk]

Thanks a lot.