Heroku "Missing Logsene Token" error even when using custom LOG_RECEIVER_URL

[jylin]

When pointing to own Elasticsearch server using "LOG_RECEIVER_URL" (or command-line flag), you should be able to specify your own index, but the Heroku listener seems to try to enforce that the index matches a regex here:
https://github.com/sematext/logagent-js/blob/master/lib/plugins/input/heroku.js#L81

It prints the error:
Error: Missing Logsene Token /asdf. Please use /LOGSENE_TOKEN.

I would like "https://myserver.herokuapp.com/asdf" to work without it having to be in the UUID format like a Sematext/Logscene token.