Use the latest version of the Guacamole Docker composition

[jsf9k]

🗣 Description

This pull request modifies the code to use the latest version of the Guacamole Docker composition.

💭 Motivation and context

The latest version of the Guacamole Docker composition uses the latest version of the cisagov/guacscanner Docker image, which itself includes the following updates to the cisagov/guacscanner repository:

• cisagov/guacscanner#32
• cisagov/guacscanner#33

🧪 Testing

Automated testing passes. I also created a new COOL staging AMI from these changes and verified that it functions as expected.

✅ Pre-approval checklist

• [x] This PR has an informative and human-readable title.
• [x] Changes are limited to a single goal - eschew scope creep!
• [x] All relevant type-of-change labels have been added.
• [x] I have read the CONTRIBUTING document.
• [x] These code changes follow cisagov code standards.
• [x] All relevant repo and/or project documentation has been updated to reflect the changes in this PR.
• [x] Tests have been added and/or modified to cover the changes in this PR.
• [x] All new and existing tests pass.

✅ Pre-merge checklist

• [x] Revert dependencies to default branches.