message: fix spell mistake
diff: @@ -149,7 +149,7 @@ def assert_same_structure(nest1, nest2, check_types=True):
  Note that namedtuples with identical name and fields are always considered
  to have the same shallow structure (even with `check_types=True`).
  - For intance, this code will print `True`:
  + For instance, this code will print `True`:
  ```python
  def nt(a, b):
  