Normalize tusooa's name

I don't have a last name and that part is solely to pass some arbitrary
name filter on some badly-implemented forge.

CONTRIBUTORS.md

@@ -11,4 +11,4 @@ Contributors of this project.
 - Vincent Guth (https://unsplash.com/photos/XrwVIFy6rTw): Background images.
 - hj (hj@shigusegubu.club): Code
 - Sean King (seanking@kazv.moe): Code
-- Tusooa Zhu (tusooa@kazv.moe): Code
+- tusooa (tusooa@kazv.moe): Code