➜  ~ sudo brew update --verbose
Password:
Error: Running Homebrew as root is extremely dangerous and no longer supported.
As Homebrew does not drop privileges on installation you would be giving all
build scripts full access to your system.
➜  ~ brew update --verbose 
Checking if we need to fetch /usr/local/Homebrew...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask...
Fetching /usr/local/Homebrew...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/homebrew/homebrew-services...
Fetching /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core...

解决方法：
不要使用 sudo