Fix Makefile variable error

Makefile

@@ -4,7 +4,7 @@ VERSION := $(shell yt --version 2> /dev/null)
 
 check:
 ifeq ($(VERSION),)
-	@echo you should use before trying anything: source /sync/Module_Dev_App_Mobile/yotta/bin/activate
+	@echo you should use before trying anything: source /sync/Module_Dev_app_mobile/yotta/bin/activate
 	@false
 endif
 
@@ -12,7 +12,7 @@ build: check
 	@yt build
 
 install: check
-	@cp build/bbc-microbit-classic-gcc/source/microbit-samples-combined.hex /media/$USER/MICROBIT/
+	@cp build/bbc-microbit-classic-gcc/source/microbit-samples-combined.hex /media/$(USER)/MICROBIT/
 	@echo "Install done"
 
 clean: check