Fix example publish to PS Gallery - Fixes #187

[PlagueHO]

Pull Request (PR) description

This PR fixes the example publish to PS Gallery by adding the missing environment variable to AppVeyor.yml. Also corrected a minor layout issue in the Changelog.md.

This Pull Request (PR) fixes the following issues

#187

Task list

• Added an entry under the Unreleased section of the CHANGELOG.md.
  Entry should say what was changed, and how that affects users (if applicable).
• Resource documentation added/updated in the resource folder.
• Resource parameter descriptions added/updated in 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.
• New/changed code adheres to DSC Resource Style Guidelines and Best Practices.

@johlju - would you mind reviewing for me? Should be a small one.

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This change is 

[codecov-io]

Codecov Report

Merging #188 into dev will not change coverage.
The diff coverage is n/a.

@@        Coverage Diff         @@
##           dev   #188   +/-   ##
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  Coverage   85%    85%           
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  Files        8      8           
  Lines      853    853           
  Branches     1      1           
==================================
  Hits       732    732           
  Misses     120    120           
  Partials     1      1

[johlju]

Reviewed 2 of 2 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved