code: async function loadConfigFile(filePath) {
    const f = await Promise.any(
      _.map(['.yml', '.yaml', '.json', ''], async(ext) =>
        await utils.fileExists(`${filePath}${ext}`)));
    if (f) {
      return loadYaml(await fs.readFileAsync(f));
    }
    return undefined;
  }
docs: if file exists, load it, else return undefined. Iterate through various possible file extensions in attempt to find file.