Merge #1303

1303: Update database.rst r=mergify[bot] a=AndreKoepke

Correct keyword for postgresql-flavor

## What type of PR?

documentation

## What does this PR do?
Fix wrong key in docs

## Prerequistes
Before we can consider review and merge, please make sure the following list is done and checked.
If an entry in not applicable, you can check it or remove it from the list.

- [ ] In case of feature or enhancement: documentation updated accordingly
- [ ] Unless it's docs or a minor change: add [changelog](https://mailu.io/master/contributors/guide.html#changelog) entry file.


Co-authored-by: AndreKoepke <andre.koepke@haw-hamburg.de>

docs/database.rst

@@ -20,7 +20,7 @@ This images has the following features:
   Useful in swarm environments, since the /data directory should not be on any network 
   filesystem (performance).
 
-To make use of this functionality, just select *Postgresql* as database flavor.
+To make use of this functionality, just select `postgresql` as database flavor.
 Don't select the usage of an external database. The ``docker-compose.yml`` and ``mailu.env``
 will pull in ``mailu/postgresql``. This image and ``mailu/admin`` contain all the scripts
 to automatically setup the database.