Fix train.py.

Author: patelrajnath

train.py

@@ -13,7 +13,7 @@
 from dl4nlp.models.cnn import CNNTagger
 from dl4nlp.models.lstm import LSTMTagger
 from dl4nlp.models.transformer import Transformer2
-from dl4nlp.models.transformer_attn import Transformer
+from dl4nlp.models.transformer_att import Transformer
 
 from dl4nlp.models.modelutils.utils import contextwin
 from dl4nlp.options import add_dataset_args, get_parser, add_model_args, add_optimization_args, add_checkpoint_args, \