Update file paths in site/en/tutorials/keras/text_classification.ipynb

[baileydauterman]

I was walking through this tutorial in Google Colab and it wasn't working quite right. Looks like there were some issues with the paths.

1. When the tar.gz was being unzipped the original dataset_dir variable was missing the _v1
2. All the training documents were nested under a aclImdb folder, so included that
3. Changed occurences of aclImdb/train to use the train_dir

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[github-actions]

Preview

Preview and run these notebook edits with Google Colab:

• site/en/tutorials/keras/text_classification.ipynb

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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

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