Upgrade to v0.18.0

I'm planning on upgrading lemmy to v0.18.0 tonight, probably around 9pm CDT. So there will be a bit of downtime, but I don't think it should take too long.

Release Announcement: https://lemmy.ca/post/862306

edit: kids baseball game went long, should start around 10pm CDT.

edit2: going to start in about 5 minutes. 9:55pm CDT.

edit3: looks like we're updated. let me know if you notice any issues!