研究两天终于在stackoverflow上找到答案了。
Failure while executing: git pull -q origin refs/heads/master:refs/remotes/origin/master
更新brew 报这个错误的时候，
You need to do the following:
cd $(brew --prefix)
rm Library/Formula/argp-standalone.rb
rm Library/Formula/cocot.rb
And then do the
git fetch origin
git reset --hard origin/master
brew update
－－－－－－－－－或者－－－－－－－－－
cd `brew --prefix`
$ git remote add origin https://github.com/Homebrew/homebrew.git
$ git fetch origin
$ git reset --hard origin/master
$ brew update
Already up-to-date.
