feat(elasticsearch): added pipeline aggregations feature to changelog

CHANGELOG.md

@@ -1,5 +1,8 @@
 # 2.6.0 (2015-12-04)
 
+### New Features
+* **Elasticsearch**: Support for pipeline aggregations Moving average and derivative, closes [#3451](https://github.com/grafana/grafana/issues/3451)
+
 ### Bug Fixes
 * **metric editors**: Fix for clicking typeahead auto dropdown option, fixes [#3428](https://github.com/grafana/grafana/issues/3428)
 * **influxdb**: Fixed issue showing Group By label only on first query, fixes [#3453](https://github.com/grafana/grafana/issues/3453)