Update changelog

CHANGELOG.md

@@ -4,6 +4,12 @@
 
 - [#4345](https://github.com/influxdata/telegraf/pull/4345): Allow for force gathering ES cluster stats.
 
+## v1.9.1 [unreleased]
+
+### Bugfixes
+
+- [#5006](https://github.com/influxdata/telegraf/issues/5006): Fix boolean handling in splunkmetric serializer.
+
 ## v1.9 [2018-11-20]
 
 #### Release Notes
@@ -73,6 +79,8 @@
 
 ## v1.8.3 [2018-10-30]
 
+### Bugfixes
+
 - [#4873](https://github.com/influxdata/telegraf/pull/4873): Add DN attributes as tags in x509_cert input to avoid series overwrite.
 - [#4921](https://github.com/influxdata/telegraf/issues/4921): Prevent connection leak by closing unused connections in amqp output.
 - [#4904](https://github.com/influxdata/telegraf/issues/4904): Use default partition key when tag does not exist in kinesis output.