Add model_max_length to config.json

config.json

@@ -20,5 +20,6 @@
   "pad_token_id": 0,
   "type_vocab_size": 2,
   "vocab_size": 69,
-  "kmer": 3
-}
+  "kmer": 3,
+  "model_max_length": 512
+}