Explicit cast from dict to str to avoid TypeError

Fix https://huggingface.co/datasets/EleutherAI/the_pile/discussions/10

the_pile.py

@@ -248,7 +248,7 @@ class ThePile(datasets.GeneratorBasedBuilder):
                         text = file.read().decode("utf-8", errors="ignore")  # encoding errors in enron_emails
                         yield key, {
                             "text": text,
-                            "meta": meta,
+                            "meta": str(meta),
                         }
                         key += 1
                 elif subset in {"uspto", "github"}: