docs: update gray color

Author: johannschopplich

README.md

@@ -4,7 +4,7 @@
 
 [![CI](https://github.com/toon-format/toon/actions/workflows/ci.yml/badge.svg)](https://github.com/toon-format/toon/actions)
 [![npm version](https://img.shields.io/npm/v/@toon-format/toon.svg)](https://www.npmjs.com/package/@toon-format/toon)
-[![SPEC v1.3](https://img.shields.io/badge/spec-v1.3-lightgrey)](https://github.com/toon-format/spec)
+[![SPEC v1.3](https://img.shields.io/badge/spec-v1.3-lightgray)](https://github.com/toon-format/spec)
 [![npm downloads (total)](https://img.shields.io/npm/dt/@toon-format/toon.svg)](https://www.npmjs.com/package/@toon-format/toon)
 [![License: MIT](https://img.shields.io/badge/license-MIT-blue.svg)](./LICENSE)