Saw this article on open vulnerabilities with the version of git on El Capitan. The gist is that apple makes it hard to even find where the binary is located – the process of actually symlinking in a new one is even more obfuscated.

I installed an upgrade with homebrew, moved the old git binary and linked in the new binary:

$ brew install git
$ sudo mv /Library/Developer/CommandLineTools/usr/bin/git /Library/Developer/CommandLineTools/usr/bin/git-apple
$ sudo ln -s /usr/local/bin/git /Library/Developer/CommandLineTools/usr/bin/git

git claims to still be in /usr/bin, but the version is now correct so it seems fine:

$ which git
/usr/bin/git
$ which git
git version 2.8.0