docs: adjust div class value for consistency (sveltejs#550)

Author: jdg2896

content/tutorial/02-advanced-svelte/07-composition/01-slots/README.md

@@ -15,7 +15,7 @@ Just like elements can have children...
 
 ```svelte
 /// file: Card.svelte
-<div class="card ">
+<div class="card">
 	+++<slot />+++
 </div>
 ```