fix

Author: chenjiahan

website/docs/en/plugins/dev/index.mdx

@@ -298,7 +298,7 @@ export const pluginEslint = (options?: Options): RsbuildPlugin => ({
 });
 ```
 
-## Extending the Plugin API
+## Extending plugin API
 
 When building custom tools on top of Rsbuild's [JavaScript API](/api/start/), you may want to extend the existing plugin API to provide additional capabilities — for example, exposing utility functions or sharing context objects.