Release 0.21.4

# History

## 0.21.4

Install/update via the bootstrap script:

```shell
wget https://raw.githubusercontent.com/dokku/dokku/v0.21.4/bootstrap.sh
sudo DOKKU_TAG=v0.21.4 bash bootstrap.sh
```

### Bug Fixes

- #4092: @Yihao-G Fix nginx proxy-read-timeout not set for HTTPS
- #4095: @GennadySpb Fix application removal during uninstallation

### New Features

- #4097: @josegonzalez Update herokuish

### Documentation

- #4096: @josegonzalez Clarify that special config variables are not exposed to applications
- #4007: @turicas Clarify nginx.conf.sigil path in image when deploying non-buildpack apps
- #4078: @gurpreetatwal Add more details to `nginx-dokku-template-source` trigger
- #4090: @ankane Official plugins no longer in beta
- #4085: @josegonzalez Set warning on resource type as an actual warning

### Other

- #4082: @dependabot-preview[bot] chore(deps): bump monolog/monolog from 1.25.4 to 1.25.5 in /tests/apps/php

docs/development/release-process.md

@@ -29,7 +29,7 @@ The workflow looks like this:
 ```shell
 # having dokku-arch in ../dokku-arch
 vagrant up build-arch
-# wait for "==> build-arch: ==> Finished making: dokku 0.21.3-2 (Mon Feb 22 23:20:37 CET 2016)"
+# wait for "==> build-arch: ==> Finished making: dokku 0.21.4-2 (Mon Feb 22 23:20:37 CET 2016)"
 cd ../dokku-arch
 git add PKGBUILD .SRCINFO
 git commit -m 'Update to dokku 0.9.9'