Fix typo in stores tutorial (#6461)

Author: Orbyt

site/content/tutorial/08-stores/02-auto-subscriptions/text.md

@@ -12,7 +12,7 @@ const unsubscribe = count.subscribe(value => {
 });
 ```
 
-You now declared `unsubscribe`, but it still needs be to called, for example through the `onDestroy` [lifecycle hook](tutorial/ondestroy):
+You now declared `unsubscribe`, but it still needs to be called, for example through the `onDestroy` [lifecycle hook](tutorial/ondestroy):
 
 ```html
 <script>