yarn 无法升级

安装官网教程安装的 yarn https://yarnpkg.com/en/docs/install#mac-stable，环境是 macos

$brew install yarn

收到警告 Warning: yarn 1.16.0 is already installed, it's just not linked
You can use `brew link yarn` to link this version.
所以就执行了

$ brew link yarn

收到信息：Linking /usr/local/Cellar/yarn/1.16.0... 
Error: Could not symlink bin/yarn
Target /usr/local/bin/yarn
already exists. You may want to remove it:
rm '/usr/local/bin/yarn'

To force the link and overwrite all conflicting files:
brew link --overwrite yarn

To list all files that would be deleted:
brew link --overwrite --dry-run yarn

然后执行了
$ rm '/usr/local/bin/yarn'
$ brew link --overwrite yarn

收到提示：Linking /usr/local/Cellar/yarn/1.16.0... 2 symlinks created

执行：$ brew upgrade yarn

得到错误：Error: yarn 1.16.0 already installed

$ yarn --version