fix Makefile dist

Makefile

@@ -71,6 +71,10 @@ run: clean build
 	@cd build && ./$(TARGET_NAME).out
 
 dist: clean
+	@if [ -z "$(TARGET_NAME)" ]; then \
+		echo "에러: 'target'을 지정해주세요.";\
+		eixt 1;\
+	fi
 	mkdir -p out
 	(cd $(SRC_DIR) && zip -9 $(TARGET_NAME).zip ./**)
 	mv $(SRC_DIR)/$(TARGET_NAME).zip out