update tokenizer - update squad example for xlnet

pytorch_transformers/tokenization_gpt2.py

@@ -185,9 +185,9 @@ class GPT2Tokenizer(PreTrainedTokenizer):
         """Converts an index (integer) in a token (string/unicode) using the vocab."""
         return self.decoder.get(index)
 
-    def _convert_ids_to_string(self, tokens_ids):
-        """Converts a sequence of ids in a string."""
-        text = ''.join(tokens_ids)
+    def convert_tokens_to_string(self, tokens):
+        """ Converts a sequence of tokens (string) in a single string. """
+        text = ''.join(tokens)
         text = bytearray([self.byte_decoder[c] for c in text]).decode('utf-8', errors=self.errors)
         return text