Depend on published vector-tile-js version

[lukasmartinelli]

Can we depend on a stable https://github.com/mapbox/vector-tile-js version?

vt2geojson/package.json

Line 22 in f5e6f1f

"vector-tile": "git+https://github.com/mapbox/vector-tile-js.git#classify-rings",

[jfirebaugh]

We'd either need to get mapbox/vector-tile-js#33 merged and do a major version release of vector-tile-js, or port that code to vt2geojson itself. My preference is the former; the ring classification code is already duplicated in several projects and it would be good not to add another.