fix({stat,readdir}/isDirectory): FileAttributes is a bit field (#69)

Fixes #68

lib/tools/stats.js

@@ -14,7 +14,7 @@ module.exports = function stat(file) {
       if (typeof attr !== 'number') {
         attr = BigInt.fromBuffer(attr).toNumber();
       }
-      return attr === DIRECTORY;
+      return (attr & DIRECTORY) == DIRECTORY;
     },
   };
 };