Update for Adam optimizer compatibility on TF 2.0

[laurauzcategui]

Fix for Update for Adam optimizer compatibility on TF 2.0

https://github.com/lmoroney/dlaicourse/issues/46

Updated:

model.compile(optimizer = tf.train.Adam(),
              loss = 'sparse_categorical_crossentropy',
              metrics=['accuracy'])

to be:

model.compile(optimizer = 'adam',
              loss = 'sparse_categorical_crossentropy',
              metrics=['accuracy'])

to fix compatibility issues with TF 2.0

[laurauzcategui]

Yet, another more elegant solution could be the convert to: tf.keras.optimizers.Adam()

I'm happy to update it, if you prefer @lmoroney 😄