minor #3633 Added missing PHP syntax coloration (DerekRoth)

This PR was submitted for the 2.4 branch but it was merged into the 2.3 branch instead (closes #3633).

Discussion
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Added missing PHP syntax coloration

Commits
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691f122 Added missing PHP syntax coloration

cookbook/security/voters_data_permission.rst

@@ -54,7 +54,7 @@ Creating the Custom Voter
 -------------------------
 
 The goal is to create a voter that checks if a user has access to view or
-edit a particular object. Here's an example implementation:
+edit a particular object. Here's an example implementation::
 
     // src/Acme/DemoBundle/Security/Authorization/Voter/PostVoter.php
     namespace Acme\DemoBundle\Security\Authorization\Voter;