Bump aws-sdk to 2.9.28
Bump aws-sdk to 2.9.28

Bumps [aws-sdk](https://github.com/aws/aws-sdk-ruby) from 2.9.27 to 2.9.28.
- [Changelog](https://github.com/aws/aws-sdk-ruby/blob/master/CHANGELOG.md)
- [Commits](https://github.com/aws/aws-sdk-ruby/compare/v2.9.27...v2.9.28)
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