Fix CHANGELOG formatting (#1230)

Author: estolfo

CHANGELOG.md

@@ -1,5 +1,5 @@
 ## 12.1.0
-- Add drop_error_types config option to not retry after certain error types [#1228](https://github.com/logstash-plugins/logstash-output-elasticsearch/pull/1228)
+ - Add drop_error_types config option to not retry after certain error types [#1228](https://github.com/logstash-plugins/logstash-output-elasticsearch/pull/1228)
 
 ## 12.0.7
  - Support both, encoded and non encoded api-key formats on plugin configuration [#1223](https://github.com/logstash-plugins/logstash-output-elasticsearch/pull/1223)