API key should be configurable

[jscheid]

The API key is currently hardwired in

react-d3-map-core/src/vectorTile.jsx

Line 71 in 80853dd

.defer(d3.json, "http://vector.mapzen.com/osm/" + layers + "/" + vectorTiles[2] + "/" + vectorTiles[0] + "/" + vectorTiles[1] + ".json?api_key=vector-tiles-_dA3ANY")

Please make it configurable so we can use our own.