Fix CI build, make CI run automatically about linfa

[bytesnake]

Glanced at travis in ndarray and they run a test script for 1.37.0, stable, beta and nightly. I'm very much in favor of Clippy

[quietlychris]

I'm not sure how I feel about clippy for scientific programming. I know that it generally recommends more "idiomatic" code, but I've seen several suggestions from it, particularly around iterators, that take code that is perhaps slightly less technically idiomatic (but much easier to interpret and maintain for humans) and turn it into an absolute mess. Other times, of course, the suggestions are great.

If we do use clippy, I might suggest it not being using the clippy::all option, and instead choose a subset of them in the CI like just clippy::correctness and clippy::complexity, and then recommending that suggestions or changes from other lints be made in the Submission Guidelines in the README.

[paulkoerbitz]

Great comments - thank you.

I've left clippy for a later PR - we can look into the changes then and (partially) have a final decision then.