git: update to v2.7.0

Update to git version v2.7.0.

* Upstream commit ed1c9977cb1b63e4270ad8bdf967a2d02580aa08 (Remove
  get_object_hash.) changed API:

  Convert all instances of get_object_hash to use an appropriate
  reference to the hash member of the oid member of struct object.
  This provides no functional change, as it is essentially a macro
  substitution.

Signed-off-by: Christian Hesse <mail@eworm.de>

ui-atom.c

@@ -19,7 +19,7 @@ static void add_entry(struct commit *commit, const char *host)
 	struct commitinfo *info;
 
 	info = cgit_parse_commit(commit);
-	hex = sha1_to_hex(commit->object.sha1);
+	hex = oid_to_hex(&commit->object.oid);
 	html("<entry>\n");
 	html("<title>");
 	html_txt(info->subject);