[Completed] Updating to 0.18.4

Lemmy 0.18.4 has been released. You can see the official release announcement here. This one's a small one so should go smoothly. As usual, we'll update at 04:00 UTC tonight.

Edit: Completed successfully as expected. Unfortunately we did have a significant downtime just before the update due to the serve running out of memory. This was partially an odd coincidence and partly my fault. I had noticed that we were getting very near being out of memory, but expected the server would hold out until we rebooted during the maintenance window tonight. Unfortunately that didn't happen. Lemmy does gradually eat memory over time and requires periodic restarts, but the frequency seems rather variable. I never had restart the server for the entire time we were running on 0.18.2, while 0.18.3 needed a restart after just a handful of days of operation. Most significantly, this incident revealed that some of my monitoring tools aren't reporting correctly. I'll be working on improving that in the future. I may also institute a periodic server restart as well. As long as I only have to restart Lemmy and not the entire server, this should be quick enough that no one will really notice.