$ brew update
       error: Your local changes to the following files would be overwritten by  merge:
        Library/Formula/erlang.rb
      Please, commit your changes or stash them before you can merge.
      Aborting
      Error: Failure while executing: git pull -q origin refs/heads/master:refs/remotes/origin/master

$ cd `brew --prefix`
$ cd Cellar/erlang/
$ git reset --hard HEAD