git-commit-tree(1): update synopsis

Even with many new kinds of options, the command still takes the
single <tree> as the first argument.

Probably we would want to update the command to allow it to take
<tree>-ish at the end for consistency.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-commit-tree.txt

@@ -10,7 +10,7 @@ SYNOPSIS
 --------
 [verse]
 'git commit-tree' <tree> [(-p <parent>)...] < changelog
-'git commit-tree' [(-p <parent>)...] [(-m <message>)...] [(-F <file>)...] <tree>
+'git commit-tree' <tree> [(-p <parent>)...] [(-m <message>)...] [(-F <file>)...]
 
 DESCRIPTION
 -----------