Extra space in kwarg unpacking

[max-sixty]

I thought I'd seen this (and maybe put an issue in already on this?) but I can't find it anywhere. So here goes:

-        return security_screen(**self.screen_kwargs)
+        return security_screen(** self.screen_kwargs)

Operating system: MacOS
Python version: 3.6.4
Black version: black, version 18.3a3
Does also happen on master: Yes

[ambv]

Thanks for your report, this is now fixed! ✨ 🍰 ✨