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

contrib/dokku-installer.py

@@ -15,7 +15,7 @@ import subprocess
 import sys
 import threading
 
-VERSION = 'v0.21.0'
+VERSION = 'v0.21.1'
 
 def bytes_to_string(b):
     if type(b) == bytes: