Installing Detectron2 onto python3.6

## Instructions To Reproduce the 🐛 Bug:
clone the detectron2 repo and try to setup.py using python3.6

```
2. What exact command you run:
python3.6 setup.py
4. __Full logs__ or other relevant observations:

https://pastebin.com/6H1QkE3A

## Expected behavior:
I was hoping detectron2 would install

## Environment:

Provide your environment information using the following command:
```
The command gives a syntax error however - Python3.6, Cuda 10.2, (Trying to get detectron2==0.6) torch==1.10.0, not sure about Cudnn, numpy==1.19.5
```

I already tried troubleshooting using common installation issues. Keep in mind I am trying to do this on a Dockerfile using Python3.6. I am also using a Jetson TX2 right now if that helps solve the issue. I know the installation works for Python3.7 however TensorRT only comes on python3.6 and it is not possible for me to rebuild it onto python3.7. Additionally, a bunch of my other installations have no support for python3.7, so it needs to be for python3.6