Added new 'delete a PR review request' feature
Added new 'delete a PR review request' feature

A new feature https://developer.github.com/v3/pulls/review_requests/#delete-a-review-request was added. This feature provide a 'delete a request for a pull request review' functionality.

pvdb/octokit.rb,JuanitoFatas/octokit.rb,octokit/octokit.rb,octokit/octokit.rb,JuanitoFatas/octokit.rb,pvdb/octokit.rb