README.md: fix MSRV badge

README.md

@@ -46,7 +46,7 @@ dual licensed as above, without any additional terms or conditions.
 [build-image]: https://github.com/RustCrypto/utils/workflows/hybrid-array/badge.svg
 [build-link]: https://github.com/RustCrypto/utils/actions/workflows/hybrid-array.yml
 [license-image]: https://img.shields.io/badge/license-Apache2.0/MIT-blue.svg
-[rustc-image]: https://img.shields.io/badge/rustc-1.65+-blue.svg
+[rustc-image]: https://img.shields.io/badge/rustc-1.81+-blue.svg
 [chat-image]: https://img.shields.io/badge/zulip-join_chat-blue.svg
 [chat-link]: https://rustcrypto.zulipchat.com/#narrow/stream/260052-utils