brew安装fatal: not in a git directory

解决办法：
执行brew -v 查看提示，homebrew-core和homebrew-cask目录 被git认为不是一个安全的目录，需要两行命令添加。

lixu@lixudeMacBook-Pro ~ % brew -v
Homebrew 3.4.1
fatal: unsafe repository ('/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core' is owned by someone else)
To add an exception for this directory, call:

	git config --global --add safe.directory /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core
Homebrew/homebrew-core (no Git repository)
fatal: unsafe repository ('/usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask' is owned by someone else)
To add an exception for this directory, call:

	git config --global --add safe.directory /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask
Homebrew/homebrew-cask (no Git repository)

根据提示在执行以下命令

git config --global --add safe.directory /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core
git config --global --add safe.directory /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask

完成