Modules Directory JSON web service: Add option for last update of the module information

It would be nice to have a URL that just returns a timestamp/date ﻿when the static/cached module JSON file was last updated. So I can decide in the new module manager that I am developing, if the local cached version of the module information should be used, or a new version should be pulled from the web.
Something like https://modules.processwire.com/export-json/?apikey=pw223&getlastupdated