fixed an indentation in the file

cc-stories.py

@@ -79,7 +79,7 @@ class Bookcorpus(datasets.GeneratorBasedBuilder):
         for _, ex in self._generate_examples(archive):
             yield ex["text"]
         
-   def _split_generators(self, dl_manager):
+    def _split_generators(self, dl_manager):
         downloaded_files = dl_manager.download_and_extract(_DATASET_URLS)
         splits = [
             datasets.SplitGenerator(