Support for rand 0.10

Hi! Would it be possible to add support for rand version 0.10? Currently, the latest version seems to be 0.10.1. Investigating this a bit, it seems that at least rand_distr would need to be updated to 0.6 as well. Also, the feature small_rng seems to have been removed.

There's also a PR for ndarray-stats for bumping rand version in that crate.