glossary: substitute "ancestor" for "direct ancestor" in 'push' description.

Even though "direct ancestor" is not defined in the glossary, the
common meaning of the term is simply "parent", parents being the only
direct ancestors, and the rest of ancestors being indirect ancestors.

As "parent" is obviously wrong in this place in the description, we
should simply say "ancestor", as everywhere else.

Signed-off-by: Sergey Organov <sorganov@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/glossary-content.txt

@@ -463,7 +463,7 @@ exclude;;
 [[def_push]]push::
 	Pushing a <<def_branch,branch>> means to get the branch's
 	<<def_head_ref,head ref>> from a remote <<def_repository,repository>>,
-	find out if it is a direct ancestor to the branch's local
+	find out if it is an ancestor to the branch's local
 	head ref, and in that case, putting all
 	objects, which are <<def_reachable,reachable>> from the local
 	head ref, and which are missing from the remote