Index: node_modules/d3-shape/src/curve/monotone.js
===================================================================
--- node_modules/d3-shape/src/curve/monotone.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-shape/src/curve/monotone.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,104 @@
+function sign(x) {
+  return x < 0 ? -1 : 1;
+}
+
+// Calculate the slopes of the tangents (Hermite-type interpolation) based on
+// the following paper: Steffen, M. 1990. A Simple Method for Monotonic
+// Interpolation in One Dimension. Astronomy and Astrophysics, Vol. 239, NO.
+// NOV(II), P. 443, 1990.
+function slope3(that, x2, y2) {
+  var h0 = that._x1 - that._x0,
+      h1 = x2 - that._x1,
+      s0 = (that._y1 - that._y0) / (h0 || h1 < 0 && -0),
+      s1 = (y2 - that._y1) / (h1 || h0 < 0 && -0),
+      p = (s0 * h1 + s1 * h0) / (h0 + h1);
+  return (sign(s0) + sign(s1)) * Math.min(Math.abs(s0), Math.abs(s1), 0.5 * Math.abs(p)) || 0;
+}
+
+// Calculate a one-sided slope.
+function slope2(that, t) {
+  var h = that._x1 - that._x0;
+  return h ? (3 * (that._y1 - that._y0) / h - t) / 2 : t;
+}
+
+// According to https://en.wikipedia.org/wiki/Cubic_Hermite_spline#Representations
+// "you can express cubic Hermite interpolation in terms of cubic Bézier curves
+// with respect to the four values p0, p0 + m0 / 3, p1 - m1 / 3, p1".
+function point(that, t0, t1) {
+  var x0 = that._x0,
+      y0 = that._y0,
+      x1 = that._x1,
+      y1 = that._y1,
+      dx = (x1 - x0) / 3;
+  that._context.bezierCurveTo(x0 + dx, y0 + dx * t0, x1 - dx, y1 - dx * t1, x1, y1);
+}
+
+function MonotoneX(context) {
+  this._context = context;
+}
+
+MonotoneX.prototype = {
+  areaStart: function() {
+    this._line = 0;
+  },
+  areaEnd: function() {
+    this._line = NaN;
+  },
+  lineStart: function() {
+    this._x0 = this._x1 =
+    this._y0 = this._y1 =
+    this._t0 = NaN;
+    this._point = 0;
+  },
+  lineEnd: function() {
+    switch (this._point) {
+      case 2: this._context.lineTo(this._x1, this._y1); break;
+      case 3: point(this, this._t0, slope2(this, this._t0)); break;
+    }
+    if (this._line || (this._line !== 0 && this._point === 1)) this._context.closePath();
+    this._line = 1 - this._line;
+  },
+  point: function(x, y) {
+    var t1 = NaN;
+
+    x = +x, y = +y;
+    if (x === this._x1 && y === this._y1) return; // Ignore coincident points.
+    switch (this._point) {
+      case 0: this._point = 1; this._line ? this._context.lineTo(x, y) : this._context.moveTo(x, y); break;
+      case 1: this._point = 2; break;
+      case 2: this._point = 3; point(this, slope2(this, t1 = slope3(this, x, y)), t1); break;
+      default: point(this, this._t0, t1 = slope3(this, x, y)); break;
+    }
+
+    this._x0 = this._x1, this._x1 = x;
+    this._y0 = this._y1, this._y1 = y;
+    this._t0 = t1;
+  }
+}
+
+function MonotoneY(context) {
+  this._context = new ReflectContext(context);
+}
+
+(MonotoneY.prototype = Object.create(MonotoneX.prototype)).point = function(x, y) {
+  MonotoneX.prototype.point.call(this, y, x);
+};
+
+function ReflectContext(context) {
+  this._context = context;
+}
+
+ReflectContext.prototype = {
+  moveTo: function(x, y) { this._context.moveTo(y, x); },
+  closePath: function() { this._context.closePath(); },
+  lineTo: function(x, y) { this._context.lineTo(y, x); },
+  bezierCurveTo: function(x1, y1, x2, y2, x, y) { this._context.bezierCurveTo(y1, x1, y2, x2, y, x); }
+};
+
+export function monotoneX(context) {
+  return new MonotoneX(context);
+}
+
+export function monotoneY(context) {
+  return new MonotoneY(context);
+}