This corrects minor remaining bits that still talked about <tree-ish>;
the Porcelain users (as opposed to plumbers) are mostly interested in
commits so use <commit> consistently and keep a sentence that mentions
that <tree-ish> can be used in place of them.
SYNOPSIS
--------
-'git-diff' [ --diff-options ] <tree-ish>{0,2} [--] [<path>...]
+'git-diff' [ --diff-options ] <commit>{0,2} [--] [<path>...]
DESCRIPTION
-----------
'git-diff' [--options] --cached [<commit>] [--] [<path>...]::
This form is to view the changes you staged for the next
- commit relative to the named <tree-ish>. Typically you
+ commit relative to the named <commit>. Typically you
would want comparison with the latest commit, so if you
do not give <commit>, it defaults to HEAD.