Update scikit-learn to 0.21.1 and and drop python2 support
Changes
- Fixed a bug in metrics.pairwise_distances where it would raise AttributeError for boolean metrics when X had a boolean dtype and Y == None.
- Fixed two bugs in metrics.pairwise_distances when n_jobs > 1.
- Fixed a bug in neighbors.KernelDensity which could not be restored from a pickle if sample_weight had been used.
- Fixed a bug where cluster.Birch could occasionally raise an AttributeError.
- Fixed a bug in cluster.KMeans where empty clusters weren’t correctly relocated when using sample weights.
- Added support for 64-bit group IDs and pointers in SVMLight files.