Updating tutorial to use sparse_softmax_cross_entropy()
Updating tutorial to use sparse_softmax_cross_entropy()

As per request from @MarkDaoust, I have updated the tutorial section of the notebook to reflect the usage of tf.losses.sparse_softmax_cross_entropy() rather than tf.losses.softmax_cross_entropy() using one-hot vectors.
tensorflow/docs-l10n,tensorflow/docs,tensorflow/docs,tensorflow/docs