Release 0.21.1

# History

## 0.21.1

Install/update via the bootstrap script:

```shell
wget https://raw.githubusercontent.com/dokku/dokku/v0.21.1/bootstrap.sh
sudo DOKKU_TAG=v0.21.1 bash bootstrap.sh
```

### Documentation

- #4060: @josegonzalez Add warning about the 0.21.0 release

docs/assets/versions.json

@@ -18,6 +18,6 @@
     "0.18.5",
     "0.19.13",
     "0.20.4",
-    "0.21.0"
+    "0.21.1"
   ]
 }