Update config.json

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

config.json

@@ -23,5 +23,6 @@
   "transformers_version": "4.20.0.dev0",
   "use_cache": true,
   "vocab_size": 50272,
-  "word_embed_proj_dim": 7168
-}
+  "word_embed_proj_dim": 7168,
+  "_remove_final_layer_norm": true
+}