peak_score.csv should probably have `k_neigh_avg` instead of `density`

[sgbaird]

Based on discussion with @hasan-sayeed

See e.g. the tutorial notebook:

disc.dens_score_df.head(10)

disc.peak_score_df.head(10)

Peak score is calculated from the kNN averages, so it's confusing that density is one of the columns in the output dataframe.