Fix help.mk awk bug (#456)

Author: davidferlay

scripts/makefile/help.mk

@@ -11,12 +11,13 @@ help:
 	@echo -e '  ${YELLOW}make${RESET} ${GREEN}<target>${RESET}'
 	@echo ''
 	@echo 'Targets:'
-	@awk '/^[a-zA-Z\-\_0-9]+:/ { \
+	@awk '/^[a-zA-Z\-_0-9]+:/ { \
 		helpMessage = match(lastLine, /^## (.*)/); \
 		if (helpMessage) { \
 			helpCommand = substr($$1, 0, index($$1, ":")); \
 			helpMessage = substr(lastLine, RSTART + 3, RLENGTH); \
 			printf "  ${YELLOW}%-$(TARGET_MAX_CHAR_NUM)s${RESET} ${GREEN}%s${RESET}\n", helpCommand, helpMessage; \
 		} \
 	} \
-	{ lastLine = $$0 }' $(MAKEFILE_LIST)
+	{ lastLine = $$0 }' $(MAKEFILE_LIST)
+