code: @Override
    public <T> OperationFuture<Boolean> touch(final String key, final int exp) {
      return touch(key, exp, transcoder);
    }
docs: Touch the given key to reset its expiration time with the default
  transcoder.
  
  @param key the key to fetch
  @param exp the new expiration to set for the given key
  @return a future that will hold the return value of whether or not the
  fetch succeeded
  @throws IllegalStateException in the rare circumstance where queue is too
  full to accept any more requests