Specify tokenizer in config.

config.json

@@ -21,6 +21,7 @@
   "pooler_num_fc_layers": 3,
   "pooler_size_per_head": 128,
   "pooler_type": "first_token_transform",
+  "tokenizer_class": "BertTokenizerFast",
   "type_vocab_size": 2,
   "vocab_size": 21128
 }