Update CHANGELOG.md

Author: andrueastman

CHANGELOG.md

@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [1.3.9] - 2024-04-17
+
+## Changed
+
+- Set default request version to be Http/2
+
 ## [1.3.8] - 2024-03-25]
 
 ## Changed
@@ -232,4 +238,4 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
-- Initial Nuget release
+- Initial Nuget release