fix minor typo on the image segmentation tutorial

[hanjihun2000]

tf.keras.losses.CategoricalCrossentropy should be changed to tf.keras.losses.SparseCategoricalCrossentropy since the pixel classes (labels) are integers, not one-hot encoded. Code is written correct, but the markdown should fix to prevent potential confusion to readers.

[github-actions]

Preview

Preview and run these notebook edits with Google Colab:

• site/en/tutorials/images/segmentation.ipynb

Rendered notebook diffs available on ReviewNB.com.

Format and style

Use the TensorFlow docs notebook tools to format for consistent source diffs and lint for style:

$ python3 -m pip install -U --user git+https://github.com/tensorflow/docs

$ python3 -m tensorflow_docs.tools.nbfmt notebook.ipynb

$ python3 -m tensorflow_docs.tools.nblint --arg=repo:tensorflow/docs notebook.ipynb

If commits are added to the pull request, synchronize your local branch: git pull origin master

[hanjihun2000]

Everything else is all perfect. Thank you for amazing image segmentation tutorial 👍

[markmcd]

LG, thanks!