fix tokenizer is not fast tokenizer issue

app.py

@@ -1,6 +1,6 @@
 import gradio as gr
 
-from transformers import GPT2Tokenizer, AutoModelForCausalLM
+from transformers import AutoTokenizer, AutoModelForCausalLM
 import numpy as np
 from transformers_cfg.grammar_utils import IncrementalGrammarConstraint
 from transformers_cfg.generation.logits_process import GrammarConstrainedLogitsProcessor
@@ -9,7 +9,7 @@ MODEL_NAME = "gpt2"
 
 if __name__ == "__main__":
     # Define your model and your tokenizer
-    tokenizer = GPT2Tokenizer.from_pretrained(MODEL_NAME)
+    tokenizer = AutoTokenizer.from_pretrained(MODEL_NAME)
     model = AutoModelForCausalLM.from_pretrained(MODEL_NAME)
     if tokenizer.pad_token_id is None:
         tokenizer.pad_token_id = tokenizer.eos_token_id