如何解决“Waiting for another flutter command to ...”

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
2020/07/26更新：

经测试，亦可通过删除 flutter 安装目录下的 bin/cache/lockfile 文件解决。

参考：
https://github.com/flutter/flutter/issues/7768
Waiting for another flutter command to release the startup lock.