Docs: Updated changelog for v6.1.3

CHANGELOG.md

 # 6.2.0 (unreleased)
 
+# 6.1.3 (unreleased)
+
+### Bug Fixes
+  * **Graph**: Fixed auto decimals in legend values for some units like `ms` and `s`. [#16455](https://github.com/grafana/grafana/pull/16455), [@torkelo](https://github.com/torkelo)
+  * **Graph**: Fixed png rendering with legend to the right. [#16463](https://github.com/grafana/grafana/pull/16463), [@torkelo](https://github.com/torkelo)
+  * **Singlestat**: Use decimals when manually specified. [#16451](https://github.com/grafana/grafana/pull/16451), [@torkelo](https://github.com/torkelo)
+  * **UI Switch**: Fix broken UI switches. Fixes Default Data Source switch, Explore Logs switches, Gauge option switches. [#16303](https://github.com/grafana/grafana/pull/16303), [@dprokop](https://github.com/dprokop)
+
 # 6.1.2 (2019-04-08)
 
  ### Bug Fixes