message: revise the format
diff: @@ -194,8 +194,7 @@ def map_fn(fn,
  * `tf.sparse.SparseTensor(st.indices, fn(st.values), st.dense_shape)`
  (if the function is expressible as TensorFlow ops)
  * `tf.sparse.SparseTensor(st.indices, tf.map_fn(fn, st.values),
  - st.dense_shape)`
  - (otherwise).
  + st.dense_shape)` (otherwise).
  #### `map_fn` vs. vectorized operations
  