fix missing import

deep_speech_2/models/model.py

@@ -10,6 +10,7 @@ import gzip
 import paddle.v2 as paddle
 from lm.lm_scorer import LmScorer
 from models.decoder import ctc_greedy_decoder, ctc_beam_search_decoder
+from models.decoder import ctc_beam_search_decoder_batch
 from models.network import deep_speech_v2_network