https://github.com/lmoroney/dlaicourse/blob/master/TensorFlow%20In%20Practice/Course%203%20-%20NLP/Course%203%20-%20Week%202%20-%20Lesson%203.ipynb
history = model.fit(train_data, epochs=num_epochs, validation_data=test_data)
hits error.
fix:
replace train_data with train_dataset
replace test_data with test_dataset