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-tree.c

@@ -287,7 +287,7 @@ void cgit_print_tree(const char *rev, char *path)
 	walk_tree_ctx.curr_rev = xstrdup(rev);
 
 	if (path == NULL) {
-		ls_tree(commit->tree->object.sha1, NULL, &walk_tree_ctx);
+		ls_tree(commit->tree->object.oid.hash, NULL, &walk_tree_ctx);
 		goto cleanup;
 	}