[ANNOUNCE] dbus-broker v21

[David Rheinsberg]

Hi

Version 21 of dbus-broker was released yesterday. It is a bugfix
release with important fixes for v20. All users are recommended to
upgrade.

Please let us know of any issues.

https://github.com/bus1/dbus-broker/releases/tag/v21

## CHANGES WITH 21:

* A handful of bugfixes for the launcher.

Contributions from: David Rheinsberg, Tom Gundersen

- Tübingen, 2019-05-02