tf_gan_on_tpus.ipynb specify TensorFlow version 1.x, update kernel to python3, and correct link

[jherberg462]

The tf_gan_on_tpus.ipynb colab notebook does not appear to be compatible with TensorFlow 2.

Using tf.compact.v1... on depreciated functionality produces a "RuntimeError: Module must be applied in the graph it was instantiated for" error.

I updated the kernel to python3 as python2 is no longer supported in colab.

The link to the GANEstimator notebook was switched to this notebook in Github. goto.google.com does not appear to be accessible to the public.

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[jherberg462]

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