Updated release notes for 1.4.8

Author: Danthar

RELEASE_NOTES.md

@@ -1,2 +1,7 @@
+#### 1.4.8 June 23 2020 ####
+
+* Updated to Akka.NET v1.4.8
+* Support for exceptions logging in non-error log levels [#109](https://github.com/akkadotnet/Akka.Logger.Serilog/pull/109)
+
 #### 1.4.3 March 27 2020 ####
 * Updated Akka.Logger.Serilog to [Akka.NET v1.4.3](https://getakka.net/community/whats-new/akkadotnet-v1.4.html)