Configuration doesn't read region from environment variable AWS_REGION

[Triforcey]

The documentation for the AWS SDK mentions being able to set the AWS region via an environment variable here. connect-dynamodb doesn't yet respect this environment variable. If the developer is unaware of this it can lead to the session table being hosted in a different region than the rest of the database.

[lancegliser]

Will need to retest this after #76 . If it stays as written the only methods for getting a client will be:

• Manual creation to pass in as client
  Fully the developer's resonsibility.
• Native new DynamoDBClient() functionality.
  I think it covers the variable you've mentioned, or at least does what developer would expect.