Switched to `JsonSerializer` / `JsonDeserializer`

[demos/kafka/wordcount] / top10

diff --git a/top10 b/top10
index b3c3b1c..aa9d59f 160000 (submodule)
--- a/top10
+++ b/top10
@@ -1 +1 @@
-Subproject commit b3c3b1c1ab19d197d323d7c69e03d9bd09147690
+Subproject commit aa9d59fa93178f40797a8bb3716dd0a30594833f