Update adversarial_keras_cnn_mnist.ipynb
Update adversarial_keras_cnn_mnist.ipynb

Updated 'tf.keras.preprocessing.image.array_to_img' to 'tf.keras.utils.array_to_img' in 'Examples of adversarially-perturbed images' section and ran the code successfully after changes.
tensorflow/neural-structured-learning,tensorflow/neural-structured-learning,tensorflow/neural-structured-learning