`librosa.filters.mel()` requires keyword args

[kaiidams]

• librosa v0.9.0 implements keyword only arguments throughout the package. Calling librosa.filters.mel() needs keywords sr, n_fft, etc. The order of keywords is the same as v0.8.1, so should be compatible with this change.
• postprocess_results() converts attr into a NumPy array, but dump_result() expects it as a Torch tensor.