message: README: Update Rust badge to 1.53+
diff: [![End to End testing][e2e-image]][e2e-link]
  [![Apache 2.0 Licensed][license-image]][license-link]
  ![Rust Stable][rustc-image]
  -![Rust 1.51+][rustc-version]
  +![Rust 1.53+][rustc-version]
  Rust implementation of the Inter-Blockchain Communication (IBC) protocol.
  @@ -38,7 +38,7 @@ Includes [TLA+ specifications](/docs/spec).
  ## Requirements
  -Developed with the latest stable version of Rust: `1.51.0`.
  +Developed with the latest stable version of Rust: `1.53.0`.
  (May work with older versions.)
  ## Hermes Guide
  @@ -107,4 +107,4 @@ Unless required by applicable law or agreed to in writing, software distributed
  [license-image]: https://img.shields.io/badge/license-Apache_2.0-blue.svg
  [license-link]: https://github.com/informalsystems/ibc-rs/blob/master/LICENSE
  [rustc-image]: https://img.shields.io/badge/rustc-stable-blue.svg
  -[rustc-version]: https://img.shields.io/badge/rustc-1.51+-blue.svg
  +[rustc-version]: https://img.shields.io/badge/rustc-1.53+-blue.svg
  