Flutter运行卡在Waiting for another flutter command to release the startup lock

执行 Flutter 包管理相关命令时有可能遇到 Waiting for another flutter command to release the startup lock... 这样的错误，可尝试杀死所有的 dart 进程解决：

// Linux
killall -9 dart

// Windows
taskkill /F /IM dart.exe

Flutter是Google的， 把 package 获取地址改为访问国内镜像站Using-Flutter-in-China

社区主镜像，采用多种方式同步 Flutter 开发者资源（推荐）

• Linux 或 Mac

export PUB_HOSTED_URL=https://pub.flutter-io.cn
export FLUTTER_STORAGE_BASE_URL=https://storage.flutter-io.cn

• Windows

PUB_HOSTED_URL ===== https://pub.flutter-io.cn
FLUTTER_STORAGE_BASE_URL ===== https://storage.flutter-io.cn

增加两个环境变量，然后执行一下 flutter doctor命令。