Prettify arrays in orm:mapping:describe command

This will prevent excessive column width and wrapping in the output which uses Symfony\Component\Console\Style\SymfonyStyle::table().

lib/Doctrine/ORM/Tools/Console/Command/MappingDescribeCommand.php

@@ -213,7 +213,7 @@ private function formatValue($value)
         }
 
         if (is_array($value)) {
-            return json_encode($value, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES);
+            return json_encode($value, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES | JSON_PRETTY_PRINT);
         }
 
         if (is_object($value)) {