use python3 for hex merge

Author: hathach

Makefile

@@ -344,23 +344,23 @@ $(BUILD)/$(OUT_FILE).out: $(BUILD) $(OBJECTS)
 
 # Create hex file (no sd, no mbr)
 $(BUILD)/$(OUT_FILE).hex: $(BUILD)/$(OUT_FILE).out
-	@echo CR $(notdir $@)
+	@echo Create $(notdir $@)
 	@$(OBJCOPY) -O ihex $< $@
 
 # Hex file with mbr (still no SD)
 $(BUILD)/$(OUT_FILE)-nosd.hex: $(BUILD)/$(OUT_FILE).hex
-	@echo CR $(notdir $@)
-	@python tools/hexmerge.py --overlap=replace -o $@ $< $(MBR_HEX)
+	@echo Create $(notdir $@)
+	@python3 tools/hexmerge.py --overlap=replace -o $@ $< $(MBR_HEX)
 
 # Bootolader only uf2
 $(BUILD)/$(OUT_FILE)-nosd.uf2: $(BUILD)/$(OUT_FILE)-nosd.hex
-	@echo CR $(notdir $@)
-	python lib/uf2/utils/uf2conv.py -f 0xd663823c -c -o $@ $^
+	@echo Create $(notdir $@)
+	@python3 lib/uf2/utils/uf2conv.py -f 0xd663823c -c -o $@ $^
 
 # merge bootloader and sd hex together
 $(BUILD)/$(MERGED_FILE).hex: $(BUILD)/$(OUT_FILE).hex
-	@echo CR $(notdir $@)
-	@python tools/hexmerge.py -o $@ $< $(SD_HEX)
+	@echo Create $(notdir $@)
+	@python3 tools/hexmerge.py -o $@ $< $(SD_HEX)
 
 # Create pkg zip file for bootloader+SD combo to use with DFU CDC
 $(BUILD)/$(MERGED_FILE).zip: $(BUILD)/$(OUT_FILE).hex