Fix README toy example incomplete var renaming
Fix README toy example incomplete var renaming

Rename of `label_probs` into `label_logprobs` in the toy example was
incomplete and, as a consequence, the toy example no longer worked. This
renames `label_probs` completely and fixes the toy example.

tensorflow/probability,tensorflow/probability,google/jax,google/jax,google/jax,google/jax