Git log.decorate can't be overridden in global config (v2.13.0)

Hi,

I recently updated to Git v2.13.0 (macOS Sierra via Homebrew), and I noticed that the default --decorate option for `git log` has changed from --decorate=no to --decorate=auto. I'd prefer to keep decoration disabled to minimize clutter in the logs, so I try disabling it in my global .gitconfig (~/.gitconfig) like so:

git config --global log.decorate none

However, this does not seem to disable the log decorations. Running `git log` again still shows the decorations. Strangely, running `git config log.decorate none` does seem to disable decoration, but I would prefer not to do this on a per-repository basis. I can only suspect that this is a Git bug, as my log.decorate global config setting is not being honored. I have already confirmed that my repository's .git/config is not overriding my global preference.

I hope this should be a simple issue, but please let me know if you have questions.

Thanks, Caleb Evans