Fix Ostinato Docstring Typo

[Sean M. Law]

In the return value for all variations of the ostinato function, the central_subseq_idx is defined as:

The subsequence index within time series Ts[central_motif_Ts_idx] the contains most central consensus motif

This should probably be:

The subsequence index within time series Ts[central_Ts_idx] that contains the most central consensus motif