Remove ES6 Map polyfill.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "d3-scale",
-  "version": "0.1.1",
+  "version": "0.1.2",
   "description": "Encodings that map abstract data to visual representation.",
   "keywords": [
     "d3",
@@ -20,12 +20,12 @@
     "url": "https://github.com/d3/d3-scale.git"
   },
   "scripts": {
-    "pretest": "mkdir -p build && d3-bundler --polyfill-map --format=umd --name=scale -- index.js > build/scale.js",
+    "pretest": "mkdir -p build && d3-bundler --format=umd --name=scale -- index.js > build/scale.js",
     "test": "TZ=America/Los_Angeles faucet `find test -name '*-test.js'`",
     "prepublish": "npm run test && uglifyjs build/scale.js -c -m -o build/scale.min.js && rm -f build/scale.zip && zip -j build/scale.zip -- LICENSE README.md build/scale.js build/scale.min.js"
   },
   "devDependencies": {
-    "d3-arrays": "~0.0.4",
+    "d3-arrays": "~0.1.1",
     "d3-bundler": "~0.2.5",
     "d3-color": "~0.2.6",
     "d3-format": "~0.3.3",

src/ordinal.js

@@ -1,3 +1,5 @@
+import {map} from "d3-arrays";
+
 function steps(length, start, step) {
   var steps = new Array(length), i = -1;
   while (++i < length) steps[i] = start + step * i;
@@ -21,7 +23,7 @@ function newOrdinal(domain, ranger) {
   scale.domain = function(x) {
     if (!arguments.length) return domain.slice();
     domain = [];
-    index = new Map;
+    index = map();
     var i = -1, n = x.length, xi, xk;
     while (++i < n) if (!index.has(xk = (xi = x[i]) + "")) index.set(xk, domain.push(xi));
     return scale[ranger.t].apply(scale, ranger.a);