Duplicated vertex in output Voronoi polygons

[jheer]

At least for the case of two input points, the returned cell polygons may duplicate the start/end-point vertex.

const points = [[10, 10], [20, 10]];
const delaunay = Delaunay.from(points);
const voronoi = d.voronoi([0, 0, 30, 20]);
console.log(voronoi.cellPolygon(0).join(' -> '));
// 15,20 -> 0,20 -> 0,0 -> 15,0 -> 15,20 -> 15,20

[mbostock]

Related #42?

[Fil]

Duplication is not detected when it happens with the first and last points.
4c2a05f#diff-2de452b04d4af7398be755b8afb55fb2R105

Not sure how to write this efficiently… not calling closePath() maybe if last===first?

[Fil]

not calling closePath() maybe if last===first?

Doing so works, but it is not so satisfying when you see the SVG path that just doesn't end with Z.
I propose instead #84