Updated SDK.CHANGELOG.md for version 3.1.0.0
Updated SDK.CHANGELOG.md for version 3.1.0.0

mwilliamson-firefly/aws-sdk-net,rafd123/aws-sdk-net,rafd123/aws-sdk-net,mwilliamson-firefly/aws-sdk-net,mwilliamson-firefly/aws-sdk-net,rafd123/aws-sdk-net