Error with using compute-fbank-feats.py
Hello! I tried to use script compute-fbank-feats.py to compute fbank features from wav, and tried to use it according to its documentation https://espnet.github.io/espnet/apis/utils_py.html#compute-fbank-feats-py

as folllows:
```
python3.7 utils/compute-fbank-feats.py scp:wav.scp ark:out.ark
```

but got an error:

```
  File "utils/compute-fbank-feats.py", line 134, in <module>
    main()
  File "utils/compute-fbank-feats.py", line 128, in main
    fmax=args.fmax,
  File "/home/karina/.local/lib/python3.7/site-packages/espnet/transform/spectrogram.py", line 116, in logmelspectrogram
    x_stft, fs=fs, n_mels=n_mels, n_fft=n_fft, fmin=fmin, fmax=fmax, eps=eps
  File "/home/karina/.local/lib/python3.7/site-packages/espnet/transform/spectrogram.py", line 74, in stft2logmelspectrogram
    fmax = fs / 2 if fmax is None else fmax
TypeError: unsupported operand type(s) for /: 'NoneType' and 'int'
```

wav.scp contains this text:
```
0 test.wav
```

Does anyone have ideas how to solve this error?
diff --git a/utils/compute-fbank-feats.py b/utils/compute-fbank-feats.py
index 72feb1800..d5defc7d8 100755
--- a/utils/compute-fbank-feats.py
+++ b/utils/compute-fbank-feats.py
@@ -118,7 +118,7 @@ def main():
 
             lmspc = logmelspectrogram(
                 x=array,
-                fs=args.fs,
+                fs=args.fs if args.fs is not None else rate,
                 n_mels=args.n_mels,
                 n_fft=args.n_fft,
                 n_shift=args.n_shift,
['utils/compute-fbank-feats.py']