Updates dynamodb.tableProps.sseEnabled documentation

[rmalecky]

Updates dynamodb.tableProps.sseEnabled documentation to reflect that all table a now encrypted[1]. When sseEnabled is true an AWS managed CMK is used, when false/default an AWS owned CMK is used.

fixes #1720

[1] https://aws.amazon.com/about-aws/whats-new/2018/11/amazon-dynamodb-encrypts-all-customer-data-at-rest/

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Pull Request Checklist

• Testing
  • Unit test added
  • CLI change?: coordinate update of integration tests with team
  • cdk-init template change?: coordinated update of integration tests with team
• Docs
  • jsdocs: All public APIs documented
  • README: README and/or documentation topic updated
• Title and Description
  • Change type: title prefixed with fix, feat will appear in changelog
  • Title: use lower-case and doesn't end with a period
  • Breaking?: last paragraph: "BREAKING CHANGE: <describe what changed + link for details>"
  • Issues: Indicate issues fixed via: "Fixes #xxx" or "Closes #xxx"
• Sensitive Modules (requires 2 PR approvers)
  • IAM Policy Document (in @aws-cdk/aws-iam)
  • EC2 Security Groups and ACLs (in @aws-cdk/aws-ec2)
  • Grant APIs (only if not based on official documentation with a reference)

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license.

[eladb]

Wow, good to know. Thanks!