Enable HTTP/2 for update checking and mapping updates

app/settings/mappingfetcher.cpp

@@ -29,6 +29,7 @@ void MappingFetcher::start()
 
     QUrl url("https://moonlight-stream.org/SDL_GameControllerDB/gamecontrollerdb.txt");
     QNetworkRequest request(url);
+    request.setAttribute(QNetworkRequest::Http2AllowedAttribute, true);
 
     // Only download the file if it's newer than what we have
     QFileInfo existingFileInfo = Path::getCacheFileInfo("gamecontrollerdb.txt");