fix example run

refraction-ray · refraction-ray · commit b1a501a00cbc · 2025-01-22T13:56:39.000+08:00
diff --git a/examples/nested_vmap_grad.py b/examples/nested_vmap_grad.py
@@ -2,7 +2,7 @@
 demonstration of vmap + grad like API
 """
 
-import os
+import sys
 
 sys.path.insert(0, "../")
 
