fixed global xhr issue

Author: fayyazarshad

packages/optimizely-sdk/lib/index.browser.tests.js

@@ -53,8 +53,8 @@ describe('javascript-sdk', function() {
         });
         sinon.spy(console, 'error');
         sinon.stub(configValidator, 'validate');
-
         xhr = sinon.useFakeXMLHttpRequest();
+        global.XMLHttpRequest = xhr;
         requests = [];
         xhr.onCreate = function(req) {
           requests.push(req);

packages/optimizely-sdk/lib/index.browser.umdtests.js

@@ -42,6 +42,7 @@ describe('javascript-sdk', function() {
         sinon.stub(Optimizely.prototype, 'close');
 
         xhr = sinon.useFakeXMLHttpRequest();
+        global.XMLHttpRequest = xhr;
         requests = [];
         xhr.onCreate = function(req) {
           requests.push(req);