minor fix

rootfs/etc/s6-overlay/scripts/80-tropoalert-init

@@ -3,7 +3,7 @@
 source /scripts/common
 s6wrap=(s6wrap --quiet --timestamps --prepend="$(basename "$0")" --args)
 
-if ! chk_enabled "$TROPOALERT"; then
+if ! chk_enabled "${TROPOALERT:-enabled}"; then
     "${s6wrap[@]}" echo "[INFO] TropoAlert is not enabled; if you want to notify when ships are received at long distance, then start container with TROPOALERT=true"
 else
     "${s6wrap[@]}" echo "[INFO] TropoAlert enabled. Checking for Tropo every ${TROPOALERT_INTERVAL:-10m}. Minimum notification distance: ${TROPO_MINDIST:-100}nm."