Update config.json

Llama2 allows 4096 context length, should be increased here.

config.json

@@ -9,7 +9,7 @@
   "hidden_size": 5120,
   "initializer_range": 0.02,
   "intermediate_size": 13824,
-  "max_position_embeddings": 2048,
+  "max_position_embeddings": 4096,
   "model_type": "llama",
   "num_attention_heads": 40,
   "num_hidden_layers": 40,