Drop the "beta" badge

README.md

@@ -5,7 +5,6 @@
 [![Tests](https://github.com/sourcefrog/cargo-mutants/actions/workflows/tests.yml/badge.svg?branch=main&event=push)](https://github.com/sourcefrog/cargo-mutants/actions/workflows/tests.yml?query=branch%3Amain)
 [![crates.io](https://img.shields.io/crates/v/cargo-mutants.svg)](https://crates.io/crates/cargo-mutants)
 [![libs.rs](https://img.shields.io/badge/libs.rs-cargo--mutants-blue)](https://lib.rs/crates/cargo-mutants)
-![Maturity: Beta](https://img.shields.io/badge/maturity-beta-blue.svg)
 
 cargo-mutants is a mutation testing tool for Rust. It helps you improve your
 program's quality by finding functions whose body could be replaced without