message: Fix docstring for `embedding_lookup_sparse`.
  Example with weighted mean combiner implies that single-key embeddings not normalized (the weighted sum answer). However, the code and test shows normalization regardless of number of keys.
diff: @@ -396,8 +396,8 @@ def embedding_lookup_sparse(params,
  with `combiner`="mean", then the output will be a 3x20 matrix where
  output[0, :] = (params[1, :] * 2.0 + params[3, :] * 0.5) / (2.0 + 0.5)
  - output[1, :] = params[0, :] * 1.0
  - output[2, :] = params[1, :] * 3.0
  + output[1, :] = (params[0, :] * 1.0) / 1.0
  + output[2, :] = (params[1, :] * 3.0) / 3.0
  Raises:
  TypeError: If sp_ids is not a SparseTensor, or if sp_weights is neither
  