Add Array.isArray polyfill for old IE

Author: Eric Wendelin

spec/spec-helper.js

@@ -1,3 +1,11 @@
+// Polyfill for old browsers
+// See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray
+if (!Array.isArray) {
+    Array.isArray = function(arg) {
+        return Object.prototype.toString.call(arg) === '[object Array]';
+    };
+}
+
 beforeEach(function() {
     this.addMatchers({
         toMatchStackFrame: function(expected) {