title: Error: A value of type 'RequestOptions' can't be assigned to a variable of type 'Future<dynamic>'
body: <p>I got below error when I compiling a  flutter project downloaded from github  .</p>
  <p>here is the code:</p>
  <pre><code>import 'package:dio/dio.dart';
  
  class HeaderInterceptors extends InterceptorsWrapper {
    @override
    onRequest(RequestOptions options) {
      // 超时
      options.connectTimeout = 15000;
      return options;
    }
  }
  </code></pre>
  <p>and here is the mistake :</p>
  <pre><code>lib/common/service/interceptors/header_interceptor.dart:8:12: Error: A value of type 'RequestOptions' can't be assigned to a variable of type 'Future&lt;dynamic&gt;'.
   - 'RequestOptions' is from 'package:dio/src/options.dart' ('/D:/intellij/flutter_windows_1.22.5-stable/flutter/.pub-cache/hosted/pub.flutter-io.cn/dio-3.0.10/lib/src/options.dart').
   - 'Future' is from 'dart:async'.
      return options;
             ^
  </code></pre>
  <p>any idea?</p>