Update quick-start.md

Update documentation to match the output of running `bun create elysia hi-elysia`

Currently, copy pasting the code from the documentation causes a `'app.server' is possibly 'null'` error, which is confusing for new users like myself

Author: Wazbat

docs/quick-start.md

@@ -40,7 +40,7 @@ const app = new Elysia()
 	.get('/', () => 'Hello Elysia')
 	.listen(8080)
 
-console.log(`🦊 Elysia is running at ${app.server.hostname}:${app.server.port}`)
+console.log(`🦊 Elysia is running at ${app.server?.hostname}:${app.server?.port}`)
 ```
 
 Start a development server by: