Switch to cisagov fork of domain-scan

[jsf9k]

🗣 Description

This pull request modifies the Docker container to use the cisagov fork of 18F/domain-scan, as well as teh latest release of cisagov/pshtt.

💭 Motivation and context

This should have been done as part of the work done around #1, but it was not.

🧪 Testing

All automated tests pass.

✅ 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] All new and existing tests pass.

✅ Pre-merge checklist

• [x] Revert dependencies to default branches.
• [x] Finalize version.

✅ Post-merge checklist

• [x] Create a release.