update broken on db_add_field

As i was not able to go through the update process by an error from the removed D7 api function of custom_breadcrumb.install line 137, changing the line with this :

db_query("ALTER TABLE custom_breadcrumb ADD COLUMN visibility_php text NOT NULL");

solved the issue, as using the db_add_field D7 function throw PDO exception even on default value set, reported here:
346006
also by removing default key from the specs array.