docs(readme): remove link to old send (#496)

Signed-off-by: Frazer Smith <[email protected]>

Author: Fdawgs

README.md

@@ -216,7 +216,7 @@ If the function returns `false`, Fastify's 404 handler will be called.
 
 Default: `undefined`
 
-Under the hood we use [send](https://github.com/pillarjs/send#index) lib that by default supports "index.html" files.
+Under the hood we use [`@fastify/send`](https://www.npmjs.com/package/@fastify/send) lib that by default supports "index.html" files.
 To disable this set false or to supply a new index pass a string or an array in preferred order.
 
 #### `serveDotFiles`