fix makefile

Makefile

@@ -3,14 +3,15 @@ publish-guide:
 	# 	if [[ "$${CURRENT_BRANCH}" != "master" ]]; then \
 	# 		echo -e "\nWarning: you're publishing the books from the 'master' branch!\n"; \
 	# 	fi
+	CURRENT_COMMIT="$$(git rev-parse --short HEAD)" && \
 	cd nimble-guide && \
 	mkdocs build && \
 	cd .. && \
 	git worktree add tmp-book gh-pages && \
 	cp -a nimble-guide/site/* tmp-book/ && \
 	cd tmp-book && \
 	git add . && { \
-		git commit -m "make publish-guide $$(git rev-parse --short HEAD)" && \
+		git commit -m "make publish-guide $${CURRENT_COMMIT}" && \
 		git push origin gh-pages || true; } && \
 	cd .. && \
 	git worktree remove -f tmp-book && \