minor #10684 Fixing typo (Geekimo)

This PR was submitted for the master branch but it was merged into the 2.8 branch instead (closes #10684).

Discussion
----------

Fixing typo

According to https://github.com/symfony/finder/blob/master/Finder.php#L38, Finder class is an IteratorAggregate

Commits
-------

376201c Fixing type

Author: javiereguiluz

components/finder.rst

@@ -51,7 +51,7 @@ the Finder instance.
 
 .. tip::
 
-    A Finder instance is a PHP :phpclass:`Iterator`. So, in addition to iterating over the
+    A Finder instance is a PHP :phpclass:`IteratorAggregate`. So, in addition to iterating over the
     Finder with ``foreach``, you can also convert it to an array with the
     :phpfunction:`iterator_to_array` function, or get the number of items with
     :phpfunction:`iterator_count`.