Mention of env var `SCAN_INTERVAL_CRON` that does not exist in RomM's code

[Cornichon622]

Hi, I'm in the process of installing RomM on my server. There are two mentions of a SCAN_INTERVAL_CRON environment variable in Scanning & Watcher however it's not mentioned in Environment Variables and it doesn't seem to exist in the code repo.

I guess it should be SCHEDULED_RESCAN_CRON instead? If somebody confirms I can make a pull request.

Thanks!