Put a space between `<' and argument in pack-objects usage string

This makes it cosistent with other places (including the
git-pack-objects(1) manpage itself) and avoids possible confusion (I,
for one, mistook `<object-list' for a `<object-list>' typo at first when
preparing this series).

Signed-off-by: Štěpán Němec <stepnem@gmail.com>
Acked-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/pack-objects.c

@@ -31,7 +31,7 @@ static const char pack_usage[] =
   "        [--threads=<n>] [--non-empty] [--revs [--unpacked | --all]]\n"
   "        [--reflog] [--stdout | base-name] [--include-tag]\n"
   "        [--keep-unreachable | --unpack-unreachable]\n"
-  "        [<ref-list | <object-list]";
+  "        [< ref-list | < object-list]";
 
 struct object_entry {
 	struct pack_idx_entry idx;