code: public <R> Try<R,Throwable> retry(final Function<? super T, ? extends R> fn) {
          return retry(fn, 7, 2, TimeUnit.SECONDS);
      }
docs: Retry a transformation if it fails. Default settings are to retry up to 7
  times, with an doubling backoff period starting @ 2 seconds delay before
  retry.
  
  
  @param fn
  Function to retry if fails