fix error: no need to flip choices for formatter type.

Form/Type/Export/PickFormatterType.php

@@ -54,7 +54,7 @@ class PickFormatterType extends AbstractType
         }
 
         $builder->add('alias', ChoiceType::class, array(
-            'choices' => array_combine(array_values($choices),array_keys($choices)),
+            'choices' => $choices,
             'choices_as_values' => true,
             'multiple' => false
         ));