normalized badges style
<div align="center">
<!-- CI status -->
<a href="https://github.com/async-rs/async-std/actions">
- <img src="https://github.com/async-rs/async-std/workflows/CI/badge.svg"
+ <img src="https://img.shields.io/github/workflow/status/async-rs/async-std/CI/main?style=flat-square"
alt="CI Status" />
</a>
<!-- Crates version -->
