dio网络代理设置办法更新

[ZhongGuanbin]

在dio5.0.1中，import 'package:dio/adapter.dart';改为了import 'package:dio/io.dart';

[ZhongGuanbin]

DefaultHttpClientAdapter弃用 @Deprecated('Use IOHttpClientAdapter instead. This will be removed in 6.0.0') typedef DefaultHttpClientAdapter = IOHttpClientAdapter;