Update RELEASE_NOTES.md
Update RELEASE_NOTES.md

added description of issue 80

Former-commit-id: bc800d4f6508a7040ac0bf9cec7f8932b99a8d88
rob-somerville/riak-dotnet-client,basho/riak-dotnet-client,rob-somerville/riak-dotnet-client,basho/riak-dotnet-client