Update reset_states() -> reset_state() in Custom Training Loops Tutorials

[james47]

As title. This is to fix the following:

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
[<ipython-input-14-e4b89749e4d3>](https://localhost:8080/#) in <cell line: 13>()
     33                          test_accuracy.result() * 100))
     34 
---> 35   test_loss.reset_states()
     36   train_accuracy.reset_states()
     37   test_accuracy.reset_states()

AttributeError: 'Mean' object has no attribute 'reset_states'

[github-actions]

Preview

Preview and run these notebook edits with Google Colab:

• site/en/tutorials/distribute/custom_training.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 james47/resetstate

[8bitmp3]

@MarkDaoust @markmcd PTAL