ghubp-username fails with recent versions of ghub

[titaniumbones]

in recent git versions of ghub, I have trouble using magithub/ghub+, because invocation of (ghub--host) fails when a parameter is absent. A fix is proposed in #15 .

[vermiculus]

Let me know if the merge fixes the issue for you; I've not been using github much at all in recent months (as I'm sure some folks have noticed…), so I'm probably not qualified to test the fix. (The change you made looks good, though, and passes tests on 26.1+.)