rand::Rand is deprecated -- update rand version and Convert to distributions::Standard

[c0gent]

TODO

[afck]

The only obstacle with that is that pairing still uses rand 0.4, so I guess

let x: Fq = rand::random();

wouldn't work anymore?

[c0gent]

I see. Ok well we might have to update it there too.

[mbr]

We (well, I) knew that rand::Rand was on the way out when I added it; I assumed we want to pick a rand (crate) version and stick to it. Using the same version as pairing seemed a logical choice.

I have no idea how easy it will be to get pairing updated to rand 0.5. Ideally, we might have gotten rid of the need for the Rand-Trait (mainly used in testing) by then.

[c0gent]

Well I've updated most of my crates that use rand to 0.5. It's mostly a find and replace but we'll have to see. Not a high priority.

[afck]

We're using rand 0.6.5 now. Closing this.