fix image sizes which were in tuple

[M-Amrollahi]

According to issue No.23, I had a minor fixes on code.

These is also a minor change needs to be applied on last cell in Notebook. I did not put it in this request because of many changes on raw ipynb file:

features, labels = data_utils.preprocess_eval(
    features,
    labels,
    max_image_size=[config.model.image_size,config.model.image_size],
    max_instances_per_image=1)

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