BBoxBlock issue with PyTorch 1.8.x

[Stijnp]

There's an issue when running nbs/course2020/vision/06_Object_Detection.ipynb using PyTorch 1.8.x.

Creating a DataBlock (with BBoxBlock and BBoxLblBlock as blocks) using the getters specified will cause some issues.

Running DataBlock.summary() will give the following error:
TypeError: no implementation found for 'torch.Tensor.getitem' on types that implement torch_function: [TensorMultiCategory, TensorBBox]

[johnyquest7]

I am facing similar problem. Previously bounding box model was working well - now it is returning all zeros