Fix anchor if it contains two or more slashes

[ksss]

Anchors are not generated correctly for cops containing two or more slashes.

For example, if you select Capybara/RSpec/PredicateMatcher from the link below, the anchor is not working.

https://github.com/rubocop/rubocop-capybara/blob/2e9e33a1feffab0c36f489387afa307a04318a66/docs/modules/ROOT/pages/cops.adoc

I have fixed it so that it does not matter how many slashes there are.

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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]

Changelog entry is not necessary due to internal modification. Can you remove it?

[koic]

Thanks!