Add the difination epoch_id before its reference

ELMo/train.py

@@ -555,6 +555,7 @@ def train_loop(args,
             valid_ppl = eval(vocab, infer_progs, dev_count, logger, args)
             logger.info("valid ppl {}".format(valid_ppl))
         if batch_id > 0 and batch_id % args.save_interval == 0:
+            epoch_id = int(batch_id / n_batches_per_epoch)
             model_path = os.path.join(args.para_save_dir,
                                       str(batch_id + epoch_id))
             if not os.path.isdir(model_path):