code: function getPullRequestFiles(resource) {
    return github.pullRequests
      .getFiles({
        owner: resource.owner,
        repo: resource.repo,
        number: resource.number,
        per_page: 100
      })
      .then(function(res) {
        return res.data;
      });
  }
docs: NB: files are either added, modified, or removed
  @param  {Object} resource - A GitHub resource
  @return {Array} An array of pull request files