fix of sed (#754)

there is no sed in-place flag that works for both linux and OSX.
the workaround is to produce a .tmp file, then developer will notice
this is the file does not need be checked in.

Makefile

@@ -107,7 +107,7 @@ clean: ## Remove all generated files
 docker-build: generate fmt vet manifests ## Build the docker image
 	docker build . -t ${IMG}
 	@echo "updating kustomize image patch file for manager resource"
-	sed -i'' -e 's@image: .*@image: '"${IMG}"'@' ./config/default/manager_image_patch.yaml
+	sed -i.tmp -e 's@image: .*@image: '"${IMG}"'@' ./config/default/manager_image_patch.yaml
 
 .PHONY: docker-push
 docker-push: ## Push the docker image