code: function getDownloadedThemes(path) {
    return new Promise((resolve, reject) => {
      const searchFile = 'bootswatch.less'
      glob('*/'+searchFile, { cwd: path }, (err, files) => {
        resolve(files.map(f => f.split('/'+searchFile)[0]).filter(f => f !== 'custom'))
      })
    })
  }
docs: Searches less file (older and newer versions include less file) inside downloaded directories and finds out which directories are belong to themes.
  @param  {String} path Working dir
  @return {Promise}     Promise to be resolved with theme names array.