message: fix a link in README.md
diff: <a href="https://www.npmjs.com/package/swc">
  <img alt="npm Downloads" src="https://img.shields.io/npm/dm/swc.svg?maxAge=43200&label=npm%20downloads">
  </a>
  - <a href="">
  - <img alt="undefined" src="https://img.shields.io/crates/d/swc_common.svg?label=crates.io%20dowloads">
  + <a href="https://crates.io/crates/swc_ecma_parser">
  + <img alt="undefined" src="https://img.shields.io/crates/d/swc_ecma_parser.svg?label=crates.io%20dowloads">
  </a>
  </p>
  <p align="center">
  