update shorturl doc

tools/goctl/rpc/gen/genlogic.go

@@ -36,11 +36,9 @@ func New{{.logicName}}(ctx context.Context,svcCtx *svc.ServiceContext) *{{.logic
 `
 	logicFunctionTemplate = `{{if .hasComment}}{{.comment}}{{end}}
 func (l *{{.logicName}}) {{.method}} (in *{{.package}}.{{.request}}) (*{{.package}}.{{.response}}, error) {
-	var resp {{.package}}.{{.response}}
-
 	// todo: add your logic here and delete this line
 	
-	return &resp,nil
+	return &{{.package}}.{{.response}}{}, nil
 }
 `
 )