_fetchPackageInstallCount = async function(packageName) {
  logger.info({ pkg: packageName }, "_fetchPackageInstallCount");
  try {
    const result = await fetchPackageMonthlyInstallCount(packageName);
    const count = result.downloads || 0;
    await PackageExtra.setMonthlyDownloads(packageName, count);
  } catch (error) {
    logger.error(
      httpErrorInfo(error, { pkg: packageName }),
      "fetch package install count error"
    );
  }
}
Fetch package install count.
@param {string} packageName