fix build

src/tables/cff/charset.rs

@@ -1,7 +1,7 @@
 use super::StringId;
 use crate::parser::{FromData, LazyArray16, Stream};
 use crate::GlyphId;
-use std::num::NonZeroU16;
+use core::num::NonZeroU16;
 
 /// The Expert Encoding conversion as defined in the Adobe Technical Note #5176 Appendix C.
 #[rustfmt::skip]