Removing unnecessary condition

lib/adapters/xhr.js

@@ -26,7 +26,6 @@ module.exports = function xhrAdapter(config) {
     // DON'T do this for testing b/c XMLHttpRequest is mocked, not XDomainRequest.
     if (process.env.NODE_ENV !== 'test' &&
         typeof window !== 'undefined' &&
-        !window.XMLHttpRequest &&
         window.XDomainRequest && !('withCredentials' in request) &&
         !isURLSameOrigin(config.url)) {
       request = new window.XDomainRequest();