Change `detectcore` function for cluster computation

[yufree]

Hi, I wonder if you could change the core detection function from detectcore() to future::availableCores() as the former function will return all the core number on the cluster node instead of the request core numbers(see details here). Meanwhile, the BiocParallel function will also use detectcore() for default settings. Thanks.

[MASHUOA]

Thanks for reminding me. The code has been modified accordingly.