Fix #970: Add extra stub to pass ConfigValidator

[dafyddcrosby]

We need to pass TargetChefVersion into the default config, otherwise the ConfigValidator#each_invalid_parameter method complains

Description

Related Issue

Types of changes

• [X] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Chore (non-breaking change that does not add functionality or fix an issue)

Checklist:

• [X] I have read the CONTRIBUTING document.
• [ ] I have run the pre-merge tests locally and they pass.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [ ] If Gemfile.lock has changed, I have used --conservative to do it and included the full output in the Description above.
• [ ] All new and existing tests passed.
• [X] All commits have been signed-off for the Developer Certificate of Origin.