Windows doesn't have a security command

[mcolyer]

Moving this from atom/atom#1035

So we currently reference the security command here src/auth.coffee

@zcbenz has opened atom/node-keytar#3, so we can replace security -q find-generic-password -ws 'GitHub API Token' with require('keytar').findPasswordForService('GitHub API Token')

On Windows ideally we should be able to get the access token from GitHub's Windows client, but @paulcbetts mentioned that Github for Windows can't use the Windows Vault due to backwards compatibility.

Given all of that, I think it still makes sense to move forward with this change because atleast if they've signed in with Atom, we can reuse that key. For initial users I think we should just suggest that they bootstrap using an environment variable. Thoughts?

[benogle]

Fixed in 0e19842