update CHANGELOG.md

Author: kaibocai

CHANGELOG.md

@@ -1,3 +1,6 @@
+## placeholder
+* Remove unused dependency `protobuf-java` to resolve CVEs ([#180](https://github.com/microsoft/durabletask-java/pull/180))
+
 ## v1.5.0
 * Fix exception type issue when using `RetriableTask` in fan in/out pattern ([#174](https://github.com/microsoft/durabletask-java/pull/174))
 * Add implementation to generate name-based deterministic UUID ([#176](https://github.com/microsoft/durabletask-java/pull/176))