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>
diff --git a/ui-plain.c b/ui-plain.c
index e4beb99..58addab 100644
--- a/ui-plain.c
+++ b/ui-plain.c
@@ -183,7 +183,7 @@
 	if (!path_items.match) {
 		path_items.match = "";
 		walk_tree_ctx.match_baselen = -1;
-		print_dir(commit->tree->object.sha1, "", 0, "");
+		print_dir(commit->tree->object.oid.hash, "", 0, "");
 		walk_tree_ctx.match = 2;
 	}
 	else