Fix an incorrect autocorrect for Style/AccessModifierDeclarations when multiple groupable access modifiers are defined

[ydah]

This PR is fix an incorrect autocorrect for Style/AccessModifierDeclarations when multiple groupable access modifiers are defined.

Code to reproduce

class Test
  private def foo; end
  private def bar; end
  def baz; end
end

Expected behavior

Automatically corrected as follows:

class Test
  def baz; end

  private

  def foo; end

  def bar; end
end

Actual behavior

Automatically corrected as follows:

class Test
  def baz; end
private

def bar; end # <--- The order is changing
private # <--- Duplicate

def foo; end # <--- The order is changing
end

---

Before submitting the PR make sure the following are checked:

• 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.

[koic]

Thanks!