[leaflet] use the earth radius value used by the s2 geometry library

this library is used in the ingress backend, so distance calculation, etc are far closer if we use the value from that

external/leaflet-src.js

@@ -1160,7 +1160,7 @@ L.LatLng.prototype = {
 	distanceTo: function (other) { // (LatLng) -> Number
 		other = L.latLng(other);
 
-		var R = 6378137, // earth radius in meters
+		var R = 6367000.0, // earth radius in meters
 		    d2r = L.LatLng.DEG_TO_RAD,
 		    dLat = (other.lat - this.lat) * d2r,
 		    dLon = (other.lng - this.lng) * d2r,
@@ -1481,7 +1481,7 @@ L.CRS.EPSG3857 = L.extend({}, L.CRS, {
 
 	project: function (latlng) { // (LatLng) -> Point
 		var projectedPoint = this.projection.project(latlng),
-		    earthRadius = 6378137;
+		    earthRadius = 6367000.0;
 		return projectedPoint.multiplyBy(earthRadius);
 	}
 });
@@ -8277,7 +8277,7 @@ L.Control.Scale = L.Control.extend({
 	_update: function () {
 		var bounds = this._map.getBounds(),
 		    centerLat = bounds.getCenter().lat,
-		    halfWorldMeters = 6378137 * Math.PI * Math.cos(centerLat * Math.PI / 180),
+		    halfWorldMeters = 6367000.0 * Math.PI * Math.cos(centerLat * Math.PI / 180),
 		    dist = halfWorldMeters * (bounds.getNorthEast().lng - bounds.getSouthWest().lng) / 180,
 
 		    size = this._map.getSize(),