renamed var to branch for continuity with steamCMD

Factorio/fctrserver

@@ -49,7 +49,8 @@ channeltag=""
 
 ## Updating | https://github.com/GameServerManagers/LinuxGSM/wiki/Update
 updateonstart="off"
-updatebranch="stable"
+# Branch: stable or experimental
+branch="stable"
 
 ## Backup | https://github.com/GameServerManagers/LinuxGSM/wiki/Backup
 maxbackups="4"