git-codereview: let codereview.cfg provide "gerrit".

Change-Id: I3b89b07dd8bb144dbfd3e502c280ed1be2f258a3
Reviewed-on: https://go-review.googlesource.com/10246
Reviewed-by: Andrew Gerrand <adg@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
1 file changed