fix variable string style

lxc-backup.sh

@@ -63,9 +63,9 @@ start_backup() {
 
   [[ -d "$backup_base" ]] || { echo "${backup_base} is not a directory"; exit 1; }
   [[ -d "$destination" ]] || mkdir "$destination"
-  [[ -f "$destination/${backup_name}" ]] && { echo "Backup already exists"; return 2; }
+  [[ -f "${destination}/${backup_name}" ]] && { echo "Backup already exists"; return 2; }
 
-  lxc export "$vm" "$destination/${backup_name}"
+  lxc export "$vm" "${destination}/${backup_name}"
 }
 
 main "$@"