Create and export ES module along side umd bundle

.eslintignore

@@ -1 +1,2 @@
 coverage/
+lib/sinon-chai.js

.eslintrc.json

@@ -6,7 +6,11 @@
     "es6": false
   },
   "parserOptions": {
-    "ecmaVersion": 5
+    "ecmaVersion": 2015,
+    "sourceType": "module",
+    "ecmaFeatures": {
+      "modules": true
+    }
   },
   "rules": {
     // Possible errors

.mocharc.js

@@ -1,5 +1,5 @@
 "use strict";
 
 module.exports = {
-    require: ["./test/common"]
+    require: ["./test/setup.mjs"]
 };

lib/sinon-chai.js → lib/sinon-chai.mjs

@@ -1,24 +1,5 @@
-"use strict";
-/* eslint-disable no-invalid-this */
-
-(function (sinonChai) {
-    // Module systems magic dance.
-
-    /* istanbul ignore else */
-    if (typeof require === "function" && typeof exports === "object" && typeof module === "object") {
-        // NodeJS
-        module.exports = sinonChai;
-    } else if (typeof define === "function" && define.amd) {
-        // AMD
-        define(function () {
-            return sinonChai;
-        });
-    } else {
-        // Other environment (usually <script> tag): plug in to global chai instance directly.
-        /* global chai: false */
-        chai.use(sinonChai);
-    }
-}(function (chai, utils) {
+
+export default function (chai, utils) {
     var slice = Array.prototype.slice;
 
     function isSpy(putativeSpy) {
@@ -146,4 +127,4 @@
     sinonMethod("calledWithMatch", "been called with arguments matching %*", "%D");
     sinonMethod("returned", "returned %1");
     exceptionalSinonMethod("thrown", "threw", "thrown %1");
-}));
+};