Update config.json

Fix config for backward compatibility with #17785

config.json

@@ -60,7 +60,7 @@
     }
   },
   "torch_dtype": "float32",
-  "transformers_version": "4.19.0.dev0",
+  "transformers_version": "4.21.0.dev0",
   "use_cache": false,
   "vocab_size": 50272
 }