Release 0.19.4

# History

## 0.19.4

Install/update via the bootstrap script:

```shell
wget https://raw.githubusercontent.com/dokku/dokku/v0.19.4/bootstrap.sh
sudo DOKKU_TAG=v0.19.4 bash bootstrap.sh
```

### Bug Fixes

- #3755: @dean1012 Warn if key_file is missing on install but do not exit

contrib/dokku-installer.py

@@ -14,7 +14,7 @@ import subprocess
 import sys
 import threading
 
-VERSION = 'v0.19.3'
+VERSION = 'v0.19.4'
 
 def bytes_to_string(b):
     if type(b) == bytes: