Release 0.18.4

# History

## 0.18.4

Install/update via the bootstrap script:

```shell
wget https://raw.githubusercontent.com/dokku/dokku/v0.18.4/bootstrap.sh
sudo DOKKU_TAG=v0.18.4 bash bootstrap.sh
```

### Other

- #3703: @scjody Update DOKKU_SCALE from Procfile during ps:scale

docs/assets/versions.json

@@ -15,6 +15,6 @@
     "0.15.5",
     "0.16.4",
     "0.17.9",
-    "0.18.3"
+    "0.18.4"
   ]
 }