Updating changelog

changelog.md

@@ -20,7 +20,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - [#705](https://github.com/Azure/azure-cosmos-dotnet-v3/pull/705) User agent suffix gets truncated
 - [#753](https://github.com/Azure/azure-cosmos-dotnet-v3/pull/753) Reason was not being propagated for Conflict exceptions
 - [#756](https://github.com/Azure/azure-cosmos-dotnet-v3/pull/756) Change Feed Processor with WithStartTime would execute the delegate the first time with no items.
-- [#769](https://github.com/Azure/azure-cosmos-dotnet-v3/pull/769) Gateway mode was updating Session Token incorrectly for some response types.
+- [#769](https://github.com/Azure/azure-cosmos-dotnet-v3/pull/769) Session Consistency + Gateway mode session-token bug fix: Under few rare non-success cases session token might be in-correct
 
 ## [3.1.1](https://www.nuget.org/packages/Microsoft.Azure.Cosmos/3.1.1) - 2019-08-12