Dio添加Cookie

在使用Options添加headers时，Map没有定义内部类型：

    Dio dio = new Dio(); Map headers = new Map(); headers['Cookie'] = cookie; Options options = new Options( headers:headers ); Future response; response = dio.get(url,options: options); 

结果请求一直失败，添加上Map内部类型的定义，请求成功。

    Dio dio = new Dio(); Map<String, dynamic> headers = new Map(); headers['Cookie'] = cookie; Options options = new Options( headers:headers ); Future response; response = dio.get(url,options: options);