【Mac】Homebrewをupdateしたら「The following untracked working tree files would be overwritten by merge:」というエラーが出た

しばらくさわってなかったMac miniのHomebrewをupdateしようとしたら以下のようなエラーが出た。

$  brew update

error: The following untracked working tree files would be overwritten by merge:
     Library/Formula/libarchive.rb
Please move or remove them before you can merge.
Aborting
Error: Failure while executing: git pull -q origin refs/heads/master:refs/remotes/origin/master

Stack Overflowの通りにやったら解決した。

http://stackoverflow.com/questions/10762859/brew-update-the-following-untracked-working-tree-files-would-be-overwritten-by

$ cd /usr/local/
$ git fetch origin
$ git reset --hard origin/master

$ brew update

参考にしたサイト

http://stackoverflow.com/questions/10762859/brew-update-the-following-untracked-working-tree-files-would-be-overwritten-by