Only return intermittent=true properties

[rmarianski]

Only return back true values, and leave off the property in the tile when it's false.

[nvkelso]

Example tile:

• http://tile.mapzen.com/mapzen/vector/v1/all/14/2615/6329.topojson

{"geometry": {"type": "Polygon", "coordinates": [[[-122.52576, 37.832308], [-122.524494, 37.832164], [-122.524378, 37.832243], [-122.524028, 37.831963], [-122.525065, 37.831664], [-122.525357, 37.831684], [-122.52576, 37.832308]]]}, "type": "Feature", "properties": {"kind": "water", "name": "Rodeo Lake", "area": 9938, "sort_rank": 200, "intermittent": false, "source": "openstreetmap.org", "min_zoom": 12.0, "id": 24656347}},...