When I intended to install ImageMagick via homebrew, and found some issues by runing
brew doctor. One was telling me that the git was out of date.
When installing Git for Mac OS via XCode, it points Git to usr/bin/git.
which git to check out the directory.
If we want to keep git up to date, we could install/upgrade git using homebrew.
Add the line in ~/.bash_profile
brew install git and
brew update git.