flutter packages get 下载不了的问题
问题描述：(This is taking an unexpectedly long time.)
解决方案：
在环境变量中配置如下命令：
FLUTTER_STORAGE_BASE_URL: https://storage.flutter-io.cn
PUB_HOSTED_URL: https://pub.flutter-io.cn
或
FLUTTER_STORAGE_BASE_URL: https://mirrors.sjtug.sjtu.edu.cn
PUB_HOSTED_URL: https://dart-pub.mirrors.sjtug.sjtu.edu.cn
