Update file-system-routing.md (#558)

Fixed formatting of the last two sections in the page. The trailingSlash section appears in the alert from scrollBehavior

Co-authored-by: Debbie O'Brien <debs-obrien@users.noreply.github.com>

content/en/guides/features/file-system-routing.md

@@ -476,7 +476,9 @@ The `scrollBehavior` option lets you define a custom behavior for the scroll p
 
 <base-alert type="next">
 
-To learn more about it, see [vue-router scrollBehavior documentation](https://router.vuejs.org/guide/advanced/scroll-behavior.html). </base-alert>
+To learn more about it, see [vue-router scrollBehavior documentation](https://router.vuejs.org/guide/advanced/scroll-behavior.html).
+
+</base-alert>
 
 Available since:v2.9.0: