Polybar: Correct secondary monitor assignment code

.config/dtfscripts/services/polybar.dtf

@@ -19,7 +19,7 @@ function start() {
 	if [[ "$secondary_monitors" == "" ]]; then
 		return 0
 	fi
-	for monitor in $secondary monitors; do
+	for monitor in $secondary_monitors; do
 		svc_log "Starting secondary on monitor $monitor"
 		PB_MONITOR=$monitor
 		polybar -r secondary& > /dev/null 2>&1