Add release date for v0.19.9

Viktor Lövgren · Viktor Lövgren · commit 2c96f079d420 · 2019-04-03T14:58:08.000+01:00
diff --git a/notes/0.19.9.markdown b/notes/0.19.9.markdown
@@ -3,3 +3,5 @@
 - Change to handle commits during rebalancing. Thanks [@CremboC](https://github.com/CremboC)! ([#117][#117])
 
 [#117]: https://github.com/ovotech/fs2-kafka/pull/117
+
+Released on 2019-04-03.
