code: function getDiffs(prs) {
    print('Fetching diffs', debug);
    return Promise.all(prs.reduce((flattenedPRs, pr) => {
      if (pr) {
        return flattenedPRs.concat(pr);
      }
    }, []).map(getDiffForPR));
  }
docs: Fetch diffs for a list of pull-requests
  @param  {Array}  repos List of pull-requests
  @return {Promise}      Resolves to an array of PRs containing diff infomation