Update installation-and-setup.mdx

Author: ZackarySantana

src/routes/solid-router/getting-started/installation-and-setup.mdx

@@ -50,7 +50,7 @@ To configure your routes, import the `Router` component and then start the appli
 import { render } from "solid-js/web";
 import { Router } from "@solidjs/router";
 
-render(() => <Router />, document.getElementById("app"));
+render(() => <Router />, document.getElementById("app")!);
 ```
 
 This sets up the router that will match on the url and render the appropriate route.