fix invoking our linter

Makefile.coq.local

@@ -12,7 +12,7 @@ style: $(VFILES) coq-lint.sh
 	$(SHOW)"Performing some style checks..."
 	$(HIDE)for FILE in $(VFILES); do \
 	  if ! fgrep -q 'From iris.prelude Require Import options.' "$$FILE"; then echo "ERROR: $$FILE does not import 'options'."; echo; exit 1; fi ; \
-	  ./coq-lint.sh "$$FILE"; \
+	  ./coq-lint.sh "$$FILE" || exit 1; \
 	done
 # Make sure main Iris does not import other Iris packages.
 	$(HIDE)if egrep 'iris\.(heap_lang|deprecated|staging)' --include "*.v" -R iris; then echo "ERROR: Iris may not import modules from other Iris packages (see above for violations)."; echo; exit 1; fi