You can also use Mapbox Studio Classic in combination with OpenMapTiles to create Tilemill2 tile styles for Mapnik renderer.
NOTE: If you need raster tiles it is highly recomended to use the TileServerGL project, which provides raster tiles rendered on server side from the vector tiles and the modern GL styles. See https://openmaptiles.org/docs/host/tileserver-gl/
Change the Source
Change the source of your TM2 style to
http://openmaptiles.org/cdn.json and save the style.
Check out the video tutorial how to port an existing TM2 style to OpenMapTiles.
Ported Classic Styles
We ported over some nice looking open licensed raster tile styles.