Fix options array key for sf2.7+

replacing choice_list by choice_loader for sf2.7+

Form/Type/ModelType.php

@@ -51,7 +51,10 @@ class ModelType extends AbstractType
     {
         if ($options['multiple']) {
             if (array_key_exists('choice_loader', $options) && $options['choice_loader'] !== null) { // SF2.7+
-                $builder->addViewTransformer(new ModelsToArrayTransformer($options['choice_list'], $options['model_manager'], $options['class']), true);
+                $builder->addViewTransformer(new ModelsToArrayTransformer(
+                    $options['choice_loader'],
+                    $options['model_manager'],
+                    $options['class']), true);
             } else {
                 $builder->addViewTransformer(new LegacyModelsToArrayTransformer($options['choice_list']), true);
             }