Correct Rubocop for private_class_method method documentation.

[bigzed]

The private_class_method modifier was not respected when checking whether a method needs documentation. I was able to fix that, but unable to fix the corresponding spec when documentation is present. Rubocop unfortunately still complains.

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• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.

[bbatsov]

I was able to fix that, but unable to fix the corresponding spec when documentation is present. Rubocop unfortunately still complains.

Can you elaborate on that? What remains to be done exactly?

[bigzed]

Sorry for the long delay. I removed the offending spec for now. The MR now only adds the private_class_method modifier to the non public modifiers and adds the corresponding spec.

The second commit I removed was testing whether a documented private_class_method def blah would register an offense and it unfortunately did. I'll revisit that and will submit a second as soon as I have fixed it.
Thank you and sorry for the delay.

[bbatsov]

The changes look good. Don't forget to reflect them in the changelog by adding a new changelog entry.

[bigzed]

@bbatsov The changelog now refelcts the bugfix under unreleased.

[bbatsov]

You shouldn't edit the changelog manually - it's generated from the files in the changelog folder at release time.

[bigzed]

Sorry, my mistake. Is this the correct way?