Update RELEASE_NOTES.md

Danthar · web-flow · commit 406bfaa74187 · 2019-10-05T20:17:06.000+02:00
diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
@@ -1,5 +1,6 @@
 #### 1.3.10 October 05 2019 ####
 * Upgraded to Serilog v2.8.0
+* Upgraded to Akka 1.3.15
 
 #### 1.3.9 August 23 2018 ####
 * [Fixed: Regression: ForContext API doesn't apply changes](https://github.com/akkadotnet/Akka.Logger.Serilog/issues/51)
