update

Makefile

@@ -1,6 +1,6 @@
 .PHONY: generate-docs
 generate-docs:
 	@cp README.md docs/index.md
-	@sed -i '' 's/\.\/CONTRIBUTING\.md/contributing\.md/g' docs/index.md
+	@sed -i 's/\.\/CONTRIBUTING\.md/contributing\.md/g' docs/index.md
 	@cp CONTRIBUTING.md docs/contributing.md
 	@go run hack/gendocs/main.go