code: function overrideUrl(url) {
    return url ? url.slice(0, url.indexOf('?')).replace(DOMAIN, CORS_FREE_DOMAIN) : null;
  }
docs: Override dropbox cloud-providers url
  https://www.dropbox.com/s/bxwwdb81z0jg7pb/keplergl_2018-11-01T23%3A22%3A43.940Z.json?dl=0
  ->
  https://dl.dropboxusercontent.com/s/bxwwdb81z0jg7pb/keplergl_2018-11-01T23%3A22%3A43.940Z.json
  @param metadata
  @returns {DropboxTypes.sharing.FileLinkMetadataReference}