changelog: adds note about closing #9399

CHANGELOG.md

@@ -27,6 +27,7 @@
 * **HTTP**: set net.Dialer.DualStack to true for all http clients [#9367](https://github.com/grafana/grafana/pull/9367)
 * **Alerting**: Add diff and percent diff as series reducers [#9386](https://github.com/grafana/grafana/pull/9386), thx [@shanhuhai5739](https://github.com/shanhuhai5739)
 * **Slack**: Allow images to be uploaded to slack when Token is precent [#7175](https://github.com/grafana/grafana/issues/7175), thx [@xginn8](https://github.com/xginn8)
+* **Opsgenie**: Use their latest API instead of old version [#9399](https://github.com/grafana/grafana/pull/9399), thx [@cglrkn](https://github.com/cglrkn)
 
 ## Tech
 * **Go**: Grafana is now built using golang 1.9