Fix update URL (#4399)

#fix https://github.com/FreshRSS/FreshRSS/issues/4395 maybe

app/Controllers/updateController.php

@@ -163,7 +163,7 @@ class FreshRSS_update_Controller extends FreshRSS_ActionController {
 				return;
 			}
 		} else {
-			$auto_update_url = FreshRSS_Context::$system_conf->auto_update_url . '?v=' . FRESHRSS_VERSION;
+			$auto_update_url = FreshRSS_Context::$system_conf->auto_update_url . '/?v=' . FRESHRSS_VERSION;
 			Minz_Log::debug('HTTP GET ' . $auto_update_url);
 			$c = curl_init($auto_update_url);
 			curl_setopt($c, CURLOPT_RETURNTRANSFER, true);