Update config.json

Fix config for backward compatibility with [#17785](https://github.com/huggingface/transformers/commit/abc400b06a8ab26cd438b6e9add3aad082ffc48f)

config.json

@@ -23,5 +23,6 @@
   "use_cache": true,
   "vocab_size": 50272,
   "word_embed_proj_dim": 768,
-  "prefix": "</s>"
-}
+  "prefix": "</s>",
+  "_remove_final_layer_norm": true
+}