Update app.py

app.py

@@ -1,5 +1,5 @@
 import os
-os.system('git clone https://github.com/facebookresearch/detectron2.git')
+os.system('git clone https://github.com/facebookresearch/detectron2.git@v0.6')
 os.system('pip install -e detectron2')
 os.system("git clone https://github.com/microsoft/unilm.git")
 os.system("sed -i 's/from collections import Iterable/from collections.abc import Iterable/' unilm/dit/object_detection/ditod/table_evaluation/data_structure.py")