fix ds2 conf for new data pipeline

examples/aishell/s0/conf/deepspeech2.yaml

@@ -3,8 +3,6 @@ data:
   train_manifest: data/manifest.train
   dev_manifest: data/manifest.dev
   test_manifest: data/manifest.test
-  mean_std_filepath: data/mean_std.json
-  vocab_filepath: data/vocab.txt 
   min_input_len: 0.0
   max_input_len: 27.0 # second
   min_output_len: 0.0
@@ -14,6 +12,9 @@ data:
 
 
 collator:
+  mean_std_filepath: data/mean_std.json
+  unit_type: char
+  vocab_filepath: data/vocab.txt 
   augmentation_config: conf/augmentation.json
   random_seed: 0
   spm_model_prefix: