core: Fix 'make dfu' message

Author: tmk

rules.mk

@@ -420,10 +420,13 @@ flip: $(TARGET).hex
 	batchisp -hardware usb -device $(MCU) -operation start reset 0
 
 dfu: $(TARGET).hex
+	@echo -n dfu-programmer: waiting
 	@until dfu-programmer atmega32u4 get bootloader-version > /dev/null 2>&1; do \
 		echo  -n "."; \
 		sleep 1; \
 	done
+	@echo
+
 ifneq (, $(findstring 0.7, $(shell dfu-programmer --version 2>&1)))
 	dfu-programmer $(MCU) erase --force
 else