docs(changelog): adds gauges to changelog

CHANGELOG.md

@@ -1,5 +1,8 @@
 # 3.0.0-beta6 (unreleased)
 
+### Enhancements
+* **Singlestat**: Support for gauges in singlestat panel. closes [#3688](https://github.com/grafana/grafana/pull/3688)
+
 ### Bug fixes
 * **InfluxDB 0.12**: Fixed issue templating and `show tag values` query only returning tags for first measurement,  fixes [#4726](https://github.com/grafana/grafana/issues/4726)
 * **Templating**: Fixed issue with regex formating when matching multiple values, fixes [#4755](https://github.com/grafana/grafana/issues/4755)