Update app.py

app.py

@@ -1,6 +1,6 @@
 # Copyright 2024-2025 The Alibaba Wan Team Authors. All rights reserved.
 # PyTorch 2.8 (temporary hack)
-import os
+import os,subprocess
 os.system('pip install --upgrade --pre --extra-index-url https://download.pytorch.org/whl/nightly/cu126 "torch<2.9" spaces')
 subprocess.run('pip install flash-attn --no-build-isolation', env={'FLASH_ATTENTION_SKIP_CUDA_BUILD': "TRUE"}, shell=True)
 import spaces