fix aarch64_neon_prefetch feature

Author: hkratz

src/lib.rs

@@ -14,6 +14,7 @@
 #![deny(missing_docs)]
 #![cfg_attr(not(feature = "std"), no_std)]
 #![cfg_attr(docsrs, feature(doc_cfg))]
+#![cfg_attr(feature = "aarch64_neon_prefetch", feature(stdarch_aarch64_prefetch))]
 
 //! Blazingly fast API-compatible UTF-8 validation for Rust using SIMD extensions, based on the implementation from
 //! [simdjson](https://github.com/simdjson/simdjson). Originally ported to Rust by the developers of [simd-json.rs](https://simd-json.rs), but now heavily improved.