The substring expansion notation is a bashism that we have not so far
adopted. Use 'git rev-parse --short' instead, as this also handles
the case where the unique abbreviation is longer than 7 characters.
Also fix the typo; the object name for submodule #2 was copied from
submodule #1's by mistake.
Suggested-by: Brandon Casey <casey@nrlssc.navy.mil> Signed-off-by: Johan Herland <johan@herland.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>