(Take 2) Fix oob index in sparse example

[ericcanton]

Re-making this PR commit after updating my Google CLA and GitHub email settings to make this commit using the email address I signed with.

From my other PR:

A sparse matrix with shape [4, 10] is being assigned an element at location [7, 0]. This changes that to the valid [3, 0].

Thanks for your time.

[github-actions]

Preview

Preview and run these notebook edits with Google Colab:

• site/en/guide/sparse_tensor.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 patch-3

[MarkDaoust]

Why isn't that an error?