Fix duplicate terminal punctuation in summary

[marcotc]

Description

This PR prevents YARD from adding a period (.) to the end of sentences that already end in a terminal punctuation character: ., ?, or !.

This is specially helpful for methods in Ruby that end with a ?, as they normally convey an interrogation:

# Has this object been successfully configured for use?
def ready?
  # ...
end

Completed Tasks

• [x] I have read the Contributing Guide.
• [x] The pull request is complete (implemented / written).
• [x] Git commits have been cleaned up (squash WIP / revert commits).
• [x] I wrote tests and ran bundle exec rake locally (if code is attached to PR).