Cancelled the XMLHttpRequest timeout callback when the request fails (fixes snowplow#348)

Author: fblundun

src/js/out_queue.js

@@ -200,6 +200,7 @@
 						clearTimeout(xhrTimeout);
 						executeQueue();
 					} else if (xhr.readyState === 4 && xhr.status >= 400) {
+						clearTimeout(xhrTimeout);
 						executingQueue = false;
 					}
 				};