Update CHANGELOG.md

CHANGELOG.md

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 # Changelog
 
-
-
-## v1.5.9 [2021-01-11]
+## Unreleased
 
 ### Bugfixes
-- [#2498](https://github.com/influxdata/kapacitor/pull/2498): avoid infinite hang when closing Kakfa writer, this also prevents the timeout error on an http update to Kafka config.
-## unreleased
-
-### BugFixes
+- [#2479](https://github.com/influxdata/kapacitor/pull/2479): Fix: influx gzip writes for large writes.
+- [#2488](https://github.com/influxdata/kapacitor/pull/2488): Fix function node name for ServiceNow handler so it is properly camelcased. 
 - [#2489](https://github.com/influxdata/kapacitor/pull/2489): Fix memory leaks in JoinNode and UnionNode.
+- [#2498](https://github.com/influxdata/kapacitor/pull/2498): Avoid infinite hang when closing Kakfa writer, this also prevents the timeout error on an http update to Kafka config.
+
+### Features
+- [#2472](https://github.com/influxdata/kapacitor/pull2472): Send full event payload on pagerduty resolve, thanks @asvinours!
+- [#2474](https://github.com/influxdata/kapacitor/pull/2491): Add barrier handling to FlattenNode.
+- [#2475](https://github.com/influxdata/kapacitor/pull/2475): Added default color theme to teams alerts, thanks @NoamShaish!
+- [#2491](https://github.com/influxdata/kapacitor/pull/2491): Fix TICKScript AST for bigpanda. 
 
 ## v1.5.8 [2021-01-11]