Node >10.17.0 support about d3-geo-polygon

[Fil]

I'd rather move forward to node-canvas@2; the change is minor:

diff --git a/test/render-world b/test/render-world
index fbc4fc4..45a79cd 100755
--- a/test/render-world
+++ b/test/render-world
@@ -10,10 +10,10 @@ if (!/^[a-z0-9]+$/i.test(projectionName)) throw new Error;

 var fs = require("fs"),
     topojson = require("topojson-client"),
-    Canvas = require("canvas"),
+    {createCanvas} = require("canvas"),
     d3 = Object.assign({}, require("d3-geo"), require("../"));

-var canvas = new Canvas(width, height),
+var canvas = createCanvas(width, height),
     context = canvas.getContext("2d");

 var world = require("world-atlas/world/50m.json"),

but the idea is to keep in sync with d3-geo and d3-geo-projection, so I'd like to ask @mbostock for his opinion first.

[Fil]

(From memory) I think it's because the tests involve node-canvas@1 and would have to be rewritten to use node-canvas@2, with its slightly different API.

[goszczynskip]

If tests are only concern here than maybe dropping this constraint is an option as short time fix. Adding preinstall step could keep local installs within a 6.x - 10.17.0 range while allowing npm usages.

[Fil]

A simpler solution at #41 (comment)

[Fil]

Related: #37

[Fil]

fixed by #41