git-unpack-objects.txt: fix inconsistent spelling of "packfile"

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-unpack-objects.txt

@@ -19,8 +19,8 @@ the objects contained within and writing them into the repository in
 "loose" (one object per file) format.
 
 Objects that already exist in the repository will *not* be unpacked
-from the pack-file.  Therefore, nothing will be unpacked if you use
-this command on a pack-file that exists within the target repository.
+from the packfile.  Therefore, nothing will be unpacked if you use
+this command on a packfile that exists within the target repository.
 
 See linkgit:git-repack[1] for options to generate
 new packs and replace existing ones.