Fix MSRV badges in the repo README

README.md

@@ -9,7 +9,7 @@ Collection of [Key Derivation Functions][KDF] (KDF) written in pure Rust.
 | Algorithm    | Crate          |                                              Crates.io                                              |                                    Documentation                                     |          MSRV           |
 |--------------|----------------|:---------------------------------------------------------------------------------------------------:|:------------------------------------------------------------------------------------:|:-----------------------:|
 | [HKDF]       | [`hkdf`]       |       [![crates.io](https://img.shields.io/crates/v/hkdf.svg)](https://crates.io/crates/hkdf)       |       [![Documentation](https://docs.rs/hkdf/badge.svg)](https://docs.rs/hkdf)       | ![MSRV 1.41][msrv-1.72] |
-| [Concat-KDF] | [`concat-kdf`] | [![crates.io](https://img.shields.io/crates/v/concat-kdf.svg)](https://crates.io/crates/concat-kdf) | [![Documentation](https://docs.rs/concat-kdf/badge.svg)](https://docs.rs/concat-kdf) | ![MSRV 1.56][msrv-1.72] |
+| [Concat-KDF] | [`concat-kdf`] | [![crates.io](https://img.shields.io/crates/v/concat-kdf.svg)](https://crates.io/crates/concat-kdf) | [![Documentation](https://docs.rs/concat-kdf/badge.svg)](https://docs.rs/concat-kdf) | ![MSRV 1.81][msrv-1.81] |
 | [ANSI-X9.63-KDF] | [`ansi-x963-kdf`] | [![crates.io](https://img.shields.io/crates/v/ansi-x963-kdf.svg)](https://crates.io/crates/ansi-x963-kdf) | [![Documentation](https://docs.rs/ansi-x963-kdf/badge.svg)](https://docs.rs/ansi-x963-kdf) | ![MSRV 1.81][msrv-1.81] |
 
 *NOTE: for password-based KDFs (e.g. Argon2, PBKDF2, scrypt), please see [RustCrypto/password-hashes]*
@@ -38,7 +38,7 @@ Unless you explicitly state otherwise, any contribution intentionally submitted
 [license-image]: https://img.shields.io/badge/license-Apache2.0/MIT-blue.svg
 [deps-image]: https://deps.rs/repo/github/RustCrypto/KDFs/status.svg
 [deps-link]: https://deps.rs/repo/github/RustCrypto/KDFs
-[msrv-1.72]: https://img.shields.io/badge/rustc-1.72+-blue.svg
+[msrv-1.81]: https://img.shields.io/badge/rustc-1.81+-blue.svg
 
 [//]: # (crates)