Update dependency to latest version: github.com/aws/aws-xray-sdk-go

[drichelson]

What does this PR do?

Update dependency: github.com/aws/aws-xray-sdk-go from v1.0.0-rc.9 to v1.4.0

Motivation

2+ years of bug fixes and improvements

Testing Guidelines

ran go test ./... locally

Additional Notes

Types of changes

• [ ] Bug fix
• [ ] New feature
• [ ] Breaking change
• [x] Misc (docs, refactoring, dependency upgrade, etc.)

Checklist

• [x] This PR's description is comprehensive
• [ ] This PR contains breaking changes that are documented in the description
• [ ] This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• [ ] This PR impacts documentation, and it has been updated (or a ticket has been logged)
• [ ] This PR's changes are covered by the automated tests
• [ ] This PR collects user input/sensitive content into Datadog

[nhinsch]

Hi @drichelson, thanks for opening this PR! We ended up incorporating this change (and a few others) into #84.