updated the release notes

Author: hneemann

distribution/ReleaseNotes.txt

@@ -1,6 +1,6 @@
 Release Notes
 
-HEAD, planned as v0.19
+v0.19, released on 14. June 2018
 - Added a tabbed pane to the attributes dialog to make it more beginner friendly.
 - Added support for asynchronous sequential circuits such as the Muller-pipeline.
   Take a look at the new asynchronous examples for illustration.