Resolves Attribute error due to Transformer version upgrade.

config.json

@@ -20,6 +20,7 @@
   "decoder_normalize_before": true,
   "decoder_start_token_id": 2,
   "decoder_vocab_size": 122672,
+  "vocab_size": 122672,
   "dropout": 0.2,
   "encoder_attention_heads": 16,
   "encoder_embed_dim": 1024,