yarn fails during cloning repo: Permission denied (publickey)

I am trying to build this project locally on my desktop with Mac OS X 10.12:
https://github.com/lionsharecapital/lionshare-desktop

When I run yarn, I get:

yarn install v0.27.5
[1/4] Resolving packages...
[2/4] Fetching packages...
error Command failed.
Exit code: 128
Command: git
Arguments: clone ssh://git@github.com/prettier/prettier.git /Users/patrick/Library/Caches/Yarn/v1/.tmp/998d9289033d5404a23434d3979d79dc
Directory: /Users/patrick/dev/lionshare-desktop
Output:
Cloning into '/Users/patrick/Library/Caches/Yarn/v1/.tmp/998d9289033d5404a23434d3979d79dc'...
Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
info Visit https://yarnpkg.com/en/docs/cli/install for documentation about this command.

Super confused, I manually ran git clone ssh://git@github.com/prettier/prettier.git /Users/patrick/Library/Caches/Yarn/v1/.tmp/998d9289033d5404a23434d3979d79d

And it worked fine... So, some how when yarn uses git, it's not making use of my global git config?

How can I fix this?

UPDATE

Trying this on a different computer strangely did not have this problem, however after installing, I did as their instructions stated:

yarn run dev

But I get:

yarn run v0.27.5
$ concurrently -k 'node desktop/server.dev.js' 'npm start'
[1] module.js:487
[1]     throw err;
[1]     ^
[1]
[1] Error: Cannot find module 'update-notifier'
[1]     at Function.Module._resolveFilename (module.js:485:15)
[1]     at Function.Module._load (module.js:437:25)
[1]     at Module.require (module.js:513:17)
[1]     at require (internal/module.js:11:18)
[1]     at /usr/local/lib/node_modules/npm/bin/npm-cli.js:29:19
[1]     at Object.<anonymous> (/usr/local/lib/node_modules/npm/bin/npm-cli.js:92:3)
[1]     at Module._compile (module.js:569:30)
[1]     at Object.Module._extensions..js (module.js:580:10)
[1]     at Module.load (module.js:503:32)
[1]     at tryModuleLoad (module.js:466:12)
[1] npm start exited with code 1
[0] listening on 3000
--> Sending SIGTERM to other processes..
[0] node desktop/server.dev.js exited with code null
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

2nd update

So apparently by running yarn, I broke npm completely, as I discovered if I attempt to do anything with npm, I get that same error:

>npm
module.js:487
    throw err;
    ^

Error: Cannot find module 'update-notifier'
    at Function.Module._resolveFilename (module.js:485:15)
    at Function.Module._load (module.js:437:25)
    at Module.require (module.js:513:17)
    at require (internal/module.js:11:18)
    at /usr/local/lib/node_modules/npm/bin/npm-cli.js:29:19
    at Object.<anonymous> (/usr/local/lib/node_modules/npm/bin/npm-cli.js:92:3)
    at Module._compile (module.js:569:30)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:503:32)
    at tryModuleLoad (module.js:466:12)

This appears to be quite a disaster!

Update 3

uninstalling node and reinstalling did not fix this, I had to remove ~/.npm, and /usr/local/lib/node_modules, then uninstall node and reinstall and now npm is working again... Geez... Any idea on how I can build this project without it breaking my development environment like this?

Solution

yarnpkg PR 2384 (yarnpkg 0.19.0) should have fixed any issue with ssh URLs.
Check if the URL should not be

git+ssh://git@github.com:prettier/prettier.git

Also, it seems to be a public repo, so you can try an https URL as well: you don't need authentication to clone said public repo.

Regarding the second error message, you can follow issue kraken-js/issues/79.
As a first workaround:

npm install -g update-notifier,