Exporting ONNX v5 from torch onnx export

I am using PyTorch 1.2 and exporting hugging face GPT-2 model into ONNX.
But, exported model is of ONNX v4 file format and is based on ONNX op version 9.
I am expecting and would like to export to v5 file format and op version 10 (i.e. ONNX 1.5.0)
How do we control exported ONNX version?
As per PyTorch 1.2 release notes (https://github.com/pytorch/pytorch/releases) this support exists.