code: func (s *PullRequestsService) IsMerged(ctx context.Context, owner string, repo string, number int) (bool, *Response, error) {
  	u := fmt.Sprintf("repos/%v/%v/pulls/%d/merge", owner, repo, number)
  	req, err := s.client.NewRequest("GET", u, nil)
  	if err != nil {
  		return false, nil, err
  	}
  
  	resp, err := s.client.Do(ctx, req, nil)
  	merged, err := parseBoolResponse(err)
  	return merged, resp, err
  }
docs: // IsMerged checks if a pull request has been merged.
  //
  // GitHub API docs: https://developer.github.com/v3/pulls/#get-if-a-pull-request-has-been-merged