Keep line breaks in list of files formatting

go/Makefile

@@ -35,7 +35,7 @@ check-formatting:
 	@output=$$(find . -path '**/vendor' -prune -or -type f -iname '*.go' ! -empty -print0 | xargs -0 grep -L "//\s*autoformat-ignore" | xargs gofmt -l 2>&1); \
 	if [ -n "$$output" ]; then \
 		echo "The following files need to be reformatted using gofmt:"; \
-		echo $$output; \
+		echo "$$output"; \
 	fi; \
 	test -z "$$output"