Bumps supported file format in anticipate of torch.div changes (#39529)
Summary:
See https://github.com/pytorch/pytorch/pull/38620 for additional context.
When PyTorch begins producing file format 4 with the updated div behavior it's safe for older PyTorch versions to consume it, since file format 4 only prohibits functionality. Bumping the supported file format version now gives PyTorch users on Master some leeway on updating their services that consume vs. produce PyTorch.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39529
Differential Revision: D21886790
Pulled By: mruberry
fbshipit-source-id: d6098eff06c26f18c3fac5cc85e5db298ba86e27
