Update streamlink-webui.sh (#4314)

Author: CrazyWolf13

ct/streamlink-webui.sh

@@ -24,7 +24,7 @@ function update_script() {
   check_container_storage
   check_container_resources
 
-  if [[ ! -f /opt/streamlink-webui ]]; then
+  if [[ ! -d /opt/streamlink-webui ]]; then
     msg_error "No ${APP} Installation Found!"
     exit
   fi