I've been a somewhat casual user of TT-RSS for several years, since Google Reader shut down (basically), but I only noticed this week that there had been no updates.
Turns out that there have been no packaged updates for a while... Two years in fact. Turns out that this forum post provided a script for performing updates, but it only pulled a couple of lines of config.
This updated script fixes that (with the config file 26).
So, this is heavily based on came88's post, and basically just fixes up some sed and adds some slightly better searching for existing values.
In your crontab, add this line (or something like it)
7 * * * * /var/www/sources/upgrade-tt-rss.sh