UI/updater: Increase number of download workers

Request / response latency dominates the download time of small
files and patches, especially the locale files. Increasing this to
4 doesn't consume many more resources and basically doubles the
download speed, especially on higher latency connections.

UI/win-update/updater/updater.cpp

@@ -1444,7 +1444,7 @@ static bool Update(wchar_t *cmdLine)
 	/* ------------------------------------- *
 	 * Download Updates                      */
 
-	if (!RunDownloadWorkers(2))
+	if (!RunDownloadWorkers(4))
 		return false;
 
 	if ((size_t)completedUpdates != updates.size()) {