write channel to config file when changed

Signed-off-by: Morris Jobke <hey@morrisjobke.de>

lib/public/Util.php

@@ -85,6 +85,7 @@ class Util {
 		//Flush timestamp to reload version.php
 		\OC::$server->getSession()->set('OC_Version_Timestamp', 0);
 		\OC::$server->getAppConfig()->setValue('core', 'OC_Channel', $channel);
+		\OC::$server->getConfig()->setSystemValue('updater.release.channel', $channel);
 	}
 	
 	/**