feat(makefile): use CGO_EXTERNAL to generate a static build (#382)

Author: lspgn

Makefile

@@ -48,7 +48,7 @@ clean:
 
 .PHONY: build
 build: prepare
-	go build -ldflags $(LDFLAGS) -o $(OUTPUT) cmd/goflow2/main.go 
+	CGO_ENABLED=0 go build -ldflags $(LDFLAGS) -o $(OUTPUT) cmd/goflow2/main.go
 
 .PHONY: docker
 docker: