flutter/packages/flutter_tools/gradle/resolve_dependencies.gradle
flutter/packages/flutter_tools/gradle/aar_init_script.gradle
flutter/packages/flutter_tools/gradle/flutter.gradle
3个文件中的 https://storage.googleapis.com/download.flutter.io
替换为：
http://download.flutter.io
或者打开”build.gradle”文件，添加“maven { url 'http://download.flutter.io' }”