fix stupid typo

app.py

@@ -74,7 +74,7 @@ def main(form):
   result['spatial_params']=spatparams
   result['distortion_params']=distparams
   result['points_params']=ptsparams
-  if 'detections' in form and isinstance(detections['form'], str):
+  if 'detections' in form and isinstance(form['detections'], str):
     result['detections']=json.loads(form['detections'])
   else:
     result['detections']=[]