Fix path to dataset in image classification tutorial

[Jberlinsky]

The image classification tutorial does not properly index into the extracted directory that contains the downloaded image dataset.

[github-actions]

Preview

Preview and run these notebook edits with Google Colab:

• site/en/tutorials/images/classification.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-1