Spaceship-prompt: Add Yarn

[cpanato]

Just to make a record here, I'm working to add Yarn :)

[cpanato]

PR: https://github.com/denysdovhan/spaceship-zsh-theme/pull/144

[denysdovhan]

What the motivation?

@cpanato I use Yarn, however I never need to know what the version I'm using at the moment.

[cpanato]

the same motivation for the docker, I use that but don't need to know the version every time. but it is good to have if need it :)

[denysdovhan]

Docker shows machine name besides its version. Sorry, but personally I consider this as useless feature. I'll keep it open for a while. Let's see if anyone would vote for it.

Maybe there's something more useful to show, related to Yarn? Not just version, but amount deps/devDeps, for example (it's better to discuss at #123). What do you think?

[cpanato]

for me the docker shows only this : 🐳 v17.03.1-ce

agree is not so useful. But for me, this is more like information item :)
Also maybe we can drop, since some friends of mine were complaining about the overall performance of spaceship and be adding more stuff will make more heavy.

thanks @denysdovhan !

[denysdovhan]

Okay, let's see how we can fit this into the new package section 🤔

[Grawl]

package displays version from package.json

but #144 is to add active Yarn package version

It's not the same

I use yvm because Yarn version less than 1.6 fails on yarn install --ignore-optional because of node-sass with error: cannot found 'are-we-there-yet', so I switch between versions on tons of my projects.