changelog: add notes about closing #12460

[skip ci]

CHANGELOG.md

@@ -11,6 +11,7 @@
 * **Table**: Make table sorting stable when null values exist [#12362](https://github.com/grafana/grafana/pull/12362), thx [@bz2](https://github.com/bz2)
 * **Prometheus**: Fix graph panel bar width issue in aligned prometheus queries [#12379](https://github.com/grafana/grafana/issues/12379)
 * **Variables**: Skip unneeded extra query request when de-selecting variable values used for repeated panels [#8186](https://github.com/grafana/grafana/issues/8186), thx [@mtanda](https://github.com/mtanda)
+* **Postgres/MySQL/MSSQL**: Use floor rounding in $__timeGroup macro function [#12460](https://github.com/grafana/grafana/issues/12460), thx [@svenklemm](https://github.com/svenklemm)
 
 # 5.2.1 (2018-06-29)