Replace npm with Yarn

[Daniel15]

No description provided.

[Daniel15]

Currently blocked by yarnpkg/yarn#1368

[tomByrer]

I suggest closing; npm5 is faster, & I don't see any substantial advantages aside form the cuter logo?
https://github.com/siddharthkp/npm-cache-benchmark

Yarn is fully deterministic as long as all your teammates are using the same Yarn version [headache]
npm has better assurances around hoisting position across npm versions
https://yarnpkg.com/blog/2017/05/31/determinism/

On personal note, Yarn was very troublesome on my Windows computer.

[Daniel15]

@tomByrer - npm5 still has a bunch of bugs so I'm not upgrading to it any time in the near future. The benchmark result isn't very convincing - a few seconds isn't going to make much of a difference. The Yarn team are currently working on Yarn 1.0. I work on Yarn myself, but mainly around the packaging/release process.

[tomByrer]

I see no issues with npm5 so far.