failure to build on architecture arm64

[alexanderkjall]

Hi

I'm packaging this crate for debian, and it fails to build on arm64 with the following error:

error[E0308]: mismatched types
   --> src/menu/wrapper.rs:166:39
    |
166 |             let _ = CString::from_raw(name);
    |                                       ^^^^ expected `u8`, found `i8`
    |
    = note: expected raw pointer `*mut u8`
               found raw pointer `*mut i8`

Full build log can be found here: https://ci.debian.net/data/autopkgtest/testing/arm64/r/rust-ncurses/5114573/log.gz

I think the correct solution should be to cast to c_char instead of i8, per this commit: https://github.com/alexanderkjall/ncurses-rs/commit/4fe1f7dc230673d48bc46c67b2522dda6a67b601

But I haven't managed to get hold of a arm64 system to test it yet.