Update config.json

The decoder_start_token_id has been forgotten for this model as well.

config.json

@@ -14,6 +14,7 @@
   "expert_capacity": 64,
   "feed_forward_proj": "relu",
   "initializer_factor": 1.0,
+  "decoder_start_token_id": 0,
   "is_encoder_decoder": true,
   "is_gated_act": false,
   "layer_norm_epsilon": 1e-06,