Fix issue with transformers library huggingface

Transformers library in the last versions verify if datasets contains a _spec_ to check if it is available

Author: alexcbb

tensorflow_datasets/core/community/huggingface_wrapper.py

@@ -27,6 +27,7 @@
 from typing import Iterator, NamedTuple, Optional, Union
 from unittest import mock
 
+from importlib.machinery import ModuleSpec
 from etils import epath
 from tensorflow_datasets.core import dataset_builder
 from tensorflow_datasets.core import dataset_info
@@ -248,7 +249,7 @@ class _MockedHFDatasets(types.ModuleType):
 
   def __init__(self):
     super().__init__('datasets')
-
+    self.__spec__  = ModuleSpec('datasets', None)
   # pylint: disable=invalid-name
 
   Version = Version