fix missing positional argument to padded_batch

[jsenellart]

When running tutorial load_data/text.ipynb with tensorflow 2.1 - the following line fails:

train_data = train_data.padded_batch(BATCH_SIZE)

with the error message:

TypeError: padded_batch() missing 1 required positional argument: 'padded_shapes'

And the document actually mentions this argument: https://www.tensorflow.org/api_docs/python/tf/data/Dataset#padded_batch.

The proposed patch adds the expected parameters with default value to pad on the text sequence.

[tfdocsbot]

Preview and run these notebook edits with Google Colab:

• site/en/tutorials/load_data/text.ipynb

Notebook diffs available on ReviewNB.com.

[MarkDaoust]

Yeah, this is causing a lot of confusion.

I added the pip install tf-nightly at the top but that's not enough.

Thanks for the PR. I'm sending a fix for all the tutorials.