Can polygraphy export *.onnx with a specific ir_version?

I run
```bash
polygraphy surgeon sanitize ./backbone.onnx --fold-constant -o backboneV2.onnx > result.txt
```
The output ONNX file is with a ir_version of 8, which is not suitable for my embedded platform (requires ir_version <= 7). 

I wonder is there a way to export *.onnx with a specific ir_version? Thanks.