contrib/subtree: there's no push --squash

The documentation says that --squash is for 'add', 'merge',
'pull' and 'push', while --squash actually doesn't change
the behavior of 'push'. Correct the documentation.

Signed-off-by: Danny Lin <danny0838@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/contrib/subtree/git-subtree.sh b/contrib/subtree/git-subtree.sh
index fa1a583..6328c87 100755
--- a/contrib/subtree/git-subtree.sh
+++ b/contrib/subtree/git-subtree.sh
Binary files differ