SecurityPolicyDsc: Fix keywords to lower-case to align with guideline

[johlju]

Pull Request (PR) description

• Changes to SecurityPolicyDsc
  • Fix keywords to lower-case to align with guideline.

This resolves a recently merged custom rule in the test framework,.

This Pull Request (PR) fixes the following issues

None

Task list

• [x] Added an entry under the Unreleased section of the change log in the README.md. Entry should say what was changed, and how that affects users (if applicable).
• [ ] Resource documentation added/updated in README.md.
• [ ] Resource parameter descriptions added/updated in README.md, schema.mof and comment-based help.
• [ ] Comment-based help added/updated.
• [ ] Localization strings added/updated in all localization files as appropriate.
• [ ] Examples appropriately added/updated.
• [ ] Unit tests added/updated. See DSC Resource Testing Guidelines.
• [ ] Integration tests added/updated (where possible). See DSC Resource Testing Guidelines.
• [x] New/changed code adheres to DSC Resource Style Guidelines and Best Practices.

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This change is 

[codecov-io]

Codecov Report

Merging #134 into dev will not change coverage. The diff coverage is 100%.

@@        Coverage Diff         @@
##           dev   #134   +/-   ##
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  Coverage   89%    89%           
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  Files        5      5           
  Lines      498    498           
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  Hits       447    447           
  Misses      51     51

[johlju]

@jcwalker this resolves a recently merged PR in the test framework that added a new custom rule.

[jcwalker]

LGTM

[jcwalker]