minor #5524 TYPO: missing closing parantheses of the array (listerical85)

This PR was merged into the 2.7 branch.

Discussion
----------

TYPO: missing closing parantheses of the array

| Q             | A
| ------------- | ---
| Doc fix?       | yes
| New docs?  | no
| Applies to    | 2.7

Fix typo: minor typo, the array was missing its closing parentheses in the code block.

Commits
-------

577087e TYPO: missing closing parantheses of the array

Author: xabbuh

cookbook/serializer.rst

@@ -169,7 +169,7 @@ to your class and choose which groups to use when serializing::
     $serializer = $this->get('serializer');
     $json = $serializer->serialize(
         $someObject,
-        'json', array('groups' => array('group1')
+        'json', array('groups' => array('group1'))
     );
 
 .. _cookbook-serializer-enabling-metadata-cache: