参考：http://flutter-dev.cn/topic/75/%E5%B7%B2%E8%A7%A3%E5%86%B3-%E5%AF%BC%E5%85%A5%E5%AE%98%E6%96%B9demo-flutter-gallery-flutter-packages-get-%E8%BF%90%E8%A1%8C%E5%87%BA%E9%94%99%E6%80%8E%E4%B9%88%E5%8A%9E
将pubspec.yaml中的https://flutter.googlesource.com/gallery-assets替换为https://gitee.com/creatint/gallery-assets.git即可解决
or
git http 代理设置：https://blog.csdn.net/daweibalang717/article/details/47613127