Update eos_token_id / bos_token_id in config.json

The current values don't appear to even be in the vocab. This makes it match the recent updates done to the tokenizer config.

config.json

@@ -9,9 +9,9 @@
     "AutoConfig": "configuration_gpt2_mq.GPT2CustomConfig",
     "AutoModelForCausalLM": "modeling_gpt2_mq.GPT2LMHeadCustomModel"
   },
-  "bos_token_id": 50256,
+  "bos_token_id": 49152,
   "embd_pdrop": 0.1,
-  "eos_token_id": 50256,
+  "eos_token_id": 49152,
   "initializer_range": 0.02,
   "layer_norm_epsilon": 1e-05,
   "model_type": "gpt2",