Beatmap creator username check is case-sensitive

[bdach]

I'm referring to the check added in #25 specifically. I'm pretty sure the same check in old BSS is also case-sensitive, but I just got a user report of a user being confused about why their map won't upload.

@peppy would appreciate your opinion on whether you see this as an actual issue that needs to be fixed (will wontfix close this if not).

[peppy]

It should be case sensitive, yes.