message: improve doc of listFiles callback
diff: @@ -533,7 +533,8 @@ function listFilesLoop(hubConfig: GaiaHubConfig,
  /**
  * List the set of files in this application's Gaia storage bucket.
  - * @param {function} callback - a callback to invoke on each named file
  + * @param {function} callback - a callback to invoke on each named file that
  + * returns `true` to continue the listing operation or `false` to end it
  * @return {Promise} that resolves to the number of files listed
  */
  export function listFiles(callback: (name: string) => boolean) : Promise<number> {
  