Index: node_modules/d3-shape/src/curve/natural.js
===================================================================
--- node_modules/d3-shape/src/curve/natural.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-shape/src/curve/natural.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,65 @@
+function Natural(context) {
+  this._context = context;
+}
+
+Natural.prototype = {
+  areaStart: function() {
+    this._line = 0;
+  },
+  areaEnd: function() {
+    this._line = NaN;
+  },
+  lineStart: function() {
+    this._x = [];
+    this._y = [];
+  },
+  lineEnd: function() {
+    var x = this._x,
+        y = this._y,
+        n = x.length;
+
+    if (n) {
+      this._line ? this._context.lineTo(x[0], y[0]) : this._context.moveTo(x[0], y[0]);
+      if (n === 2) {
+        this._context.lineTo(x[1], y[1]);
+      } else {
+        var px = controlPoints(x),
+            py = controlPoints(y);
+        for (var i0 = 0, i1 = 1; i1 < n; ++i0, ++i1) {
+          this._context.bezierCurveTo(px[0][i0], py[0][i0], px[1][i0], py[1][i0], x[i1], y[i1]);
+        }
+      }
+    }
+
+    if (this._line || (this._line !== 0 && n === 1)) this._context.closePath();
+    this._line = 1 - this._line;
+    this._x = this._y = null;
+  },
+  point: function(x, y) {
+    this._x.push(+x);
+    this._y.push(+y);
+  }
+};
+
+// See https://www.particleincell.com/2012/bezier-splines/ for derivation.
+function controlPoints(x) {
+  var i,
+      n = x.length - 1,
+      m,
+      a = new Array(n),
+      b = new Array(n),
+      r = new Array(n);
+  a[0] = 0, b[0] = 2, r[0] = x[0] + 2 * x[1];
+  for (i = 1; i < n - 1; ++i) a[i] = 1, b[i] = 4, r[i] = 4 * x[i] + 2 * x[i + 1];
+  a[n - 1] = 2, b[n - 1] = 7, r[n - 1] = 8 * x[n - 1] + x[n];
+  for (i = 1; i < n; ++i) m = a[i] / b[i - 1], b[i] -= m, r[i] -= m * r[i - 1];
+  a[n - 1] = r[n - 1] / b[n - 1];
+  for (i = n - 2; i >= 0; --i) a[i] = (r[i] - a[i + 1]) / b[i];
+  b[n - 1] = (x[n] + a[n - 1]) / 2;
+  for (i = 0; i < n - 1; ++i) b[i] = 2 * x[i + 1] - a[i + 1];
+  return [a, b];
+}
+
+export default function(context) {
+  return new Natural(context);
+}