Update librosa calls to fix argument errors.

[peacheym]

Currently the calls to librosa that handle onset detection breaks the timbral_extractor(...). Explicitly passing arguments fixes the issue.

[gionstegmann]

Hi @brayanrodbajo,

I noticed that this pull request has been approved but hasn't been merged yet, although the modifications provided by @peacheym seem to solve the issue. Could we get an update on the status of this merge?