Add "did you mean" message when failing due to invalid cops in configuration

[dvandersluis]

Try to suggest a replacement cop when an invalid cop name is found in the config.

eg:

Error: unrecognized cop Layout/LyneLenth found in .rubocop.yml
Did you mean `Layout/LineLength`?
unrecognized cop Lint/LiteralInCondition found in .rubocop.yml
Did you mean `Lint/LiteralAsCondition`?

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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.

[bbatsov]

Cool idea! I love it!