ImportError: cannot import name normalize_data_format

[SeekPoint]

ub16hp@UB16HP:/ub16_prj/BiLstm_CNN_CRF_CWS/simple_bilstm_model$ python bilstm__cnn_crf.py
Using TensorFlow backend.
Traceback (most recent call last):
File "bilstm__cnn_crf.py", line 27, in
from keras_contrib.layers import CRF
File "/usr/local/lib/python2.7/dist-packages/keras_contrib/init.py", line 4, in
from . import layers
File "/usr/local/lib/python2.7/dist-packages/keras_contrib/layers/init.py", line 3, in
from .convolutional import *
File "/usr/local/lib/python2.7/dist-packages/keras_contrib/layers/convolutional.py", line 15, in
from keras.backend.common import normalize_data_format
ImportError: cannot import name normalize_data_format
ub16hp@UB16HP:/ub16_prj/BiLstm_CNN_CRF_CWS/simple_bilstm_model$