more polyfills for the browser

package.json

@@ -7,7 +7,11 @@
   "scripts": {
     "test": "make lint test",
     "bundle": "webpack --output-library fetchMock --entry ./es5/client.js --output-filename ./es5/client-bundle.js",
-    "prepublish": "babel src --out-dir es5 --presets env --plugins transform-runtime && npm run bundle"
+    "prepublish": "babel src --out-dir es5 && npm run bundle"
+  },
+  "babel": {
+    "presets": [["env", {"useBuiltIns": "entry"}]],
+    "plugins": [["transform-runtime", {"polyfill": true}]]
   },
   "repository": {
     "type": "git",
@@ -36,6 +40,7 @@
     "babel-cli": "^6.1.2",
     "babel-loader": "^7.1.2",
     "babel-plugin-transform-runtime": "^6.23.0",
+    "babel-polyfill": "^6.26.0",
     "babel-preset-env": "^1.6.1",
     "bluebird": "^3.4.6",
     "chai": "^4.1.2",
@@ -46,8 +51,8 @@
     "karma-chai": "^0.1.0",
     "karma-chrome-launcher": "^2.2.0",
     "karma-mocha": "^1.3.0",
-    "karma-webpack": "^2.0.9",
     "karma-mocha-reporter": "^2.2.5",
+    "karma-webpack": "^2.0.9",
     "mocha": "^4.0.1",
     "node-fetch": "^2.0.0-alpha.9",
     "sinon": "^4.1.3",

src/client.js

@@ -1,3 +1,4 @@
+require('babel-polyfill');
 const FetchMock = require('./lib/index');
 const statusTextMap = require('./lib/status-text');
 const theGlobal = typeof window !== 'undefined' ? window : self;
@@ -12,4 +13,4 @@ FetchMock.config = Object.assign(FetchMock.config, {
 	Headers: theGlobal.Headers
 });
 
-module.exports = FetchMock.createInstance();
+module.exports = FetchMock.createInstance();