gc: remove trailing dot from "gc.log" line

gc: remove trailing dot from "gc.log" line

Remove the trailing dot from the warning we emit about gc.log. It's
common for various terminal UX's to allow the user to select "words",
and by including the trailing dot a user wanting to select the path to
gc.log will need to manually remove the trailing dot.

Such a user would also probably need to adjust the path if it e.g. had
spaces in it, but this should address this very common case.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Suggested-by: Jan Judas <snugar.i@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>