Fix blank sections of the Delaware River.

assets/styles/mapzen.xml
	-Sections of the Delaware River between Philadelphia and Camden
	(example tile: 18/76454/99215) weren't being rendered.
	-OpenScienceMap presumably wouldn't render anything when faced
	with polygons with identical geometry and identical properties
	(it only matches up to `k="kind" v="riverbank"`, which matches
	both polys).
	-Thus, add a more specific match for any polygons with a `name`
	key, which only one of the polygons has. Allows the renderer to
	choose one over the other(s).