fix: explicitly set XHR to async mode (#1834)

Some sites (Shopify) monkey patch a default synchronous XHR which causes
RudderStack SDK to crash because it's providing a `timeout` expecting
XHR to default to async mode.

packages/analytics-js/src/services/HttpClient/xhr/xhrRequestHandler.ts

@@ -115,7 +115,7 @@ const xhrRequest = (
       }
     };
 
-    xhr.open(options.method, options.url);
+    xhr.open(options.method, options.url, true);
     if (options.withCredentials === true) {
       xhr.withCredentials = true;
     }