minor symfony#8131 fixed syntax in choice.rst regarding choice_loader (scuben)

This PR was submitted for the 3.3 branch but it was merged into the 3.2 branch instead (closes symfony#8131).

Discussion
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fixed syntax in choice.rst regarding choice_loader

Commits
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87b89ca fixed typo in choice.rst regarding choice_loader

Author: xabbuh

reference/forms/types/choice.rst

@@ -198,7 +198,7 @@ if you want to take advantage of lazy loading::
     $builder->add('constants', ChoiceType::class, array(
         'choice_loader' => new CallbackChoiceLoader(function() {
             return StaticClass::getConstants();
-        },
+        }),
     ));
 
 This will cause the call of ``StaticClass::getConstants()`` to not happen if the