Fixed failing fallback of the environment.

Author: BluePsyduck

config/config.php

@@ -38,7 +38,7 @@
     //   - `*.global.php`
     //   - `[FIB_ENV]/*.local.php`
     new PhpFileProvider(
-        realpath(__DIR__) . sprintf('/autoload/{*.global.php,%s/*.local.php}', getenv('FIB_ENV') ?? 'production'),
+        realpath(__DIR__) . sprintf('/autoload/{*.global.php,%s/*.local.php}', getenv('FIB_ENV') ?: 'production'),
     ),
 ], $cacheConfig['config_cache_path']);