CRM-12647 - Fix misnamed variable

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* CRM-12647: Customization export/import crashes on "&"
  http://issues.civicrm.org/jira/browse/CRM-12647

CRM/Utils/Migrate/Export.php

@@ -357,7 +357,7 @@ AND    entity_id    IS NULL
             }
             $keyValues['extends_entity_column_value_option_group'] = $key;
             $types = explode(CRM_Core_DAO::VALUE_SEPARATOR, substr($object->$name, 1, -1));
-            $value = array();
+            $values = array();
             foreach ($types as $type) {
               $values[] = $this->_xml['optionValue']['map']["$key.{$type}"];
             }