Fix configuration key

Author: theofidry

src/Configuration.php

@@ -50,7 +50,7 @@ class Configuration
         self::PATCHERS_KEYWORD,
         self::WHITELIST_KEYWORD,
         self::WHITELIST_GLOBAL_CONSTANTS_KEYWORD,
-        self::WHITELIST_GLOBAL_FUNCTIONS_KEYWORD,
+        self::WHITELIST_GLOBAL_CLASSES_KEYWORD,
         self::WHITELIST_GLOBAL_FUNCTIONS_KEYWORD,
     ];