better error message for "account disabled" response from server

[shiftkey]

From https://github.com/desktop/desktop/issues/6538#issuecomment-452350468

Cloning into '/Users/***/***/***'...
remote: Your account is disabled. Please see https://github.com/account/billing
fatal: unable to access 'https://github.com/***/***.git/': The requested URL returned error: 403

[zerefwayne]

Hi @shiftkey, is this project under active development? I would love to contribute to this.

[shiftkey]

@zerefwayne go for it!

[shiftkey]

@zerefwayne check out one of our previous PRs that add new error codes, e.g. #105