osx brew won't update, solution found

Problem:
$ brew update
error: Your local changes to the following files would be overwritten by merge:
share/man/man1/brew.1
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

Solution:
chmod 644 /usr/local/share/man/man1/brew.1

Source:
https://github.com/mxcl/homebrew/issues/13581#issuecomment-9751497