restore py37

hivemind/utils/autograd.py

@@ -94,4 +94,4 @@ class _ParallelApplyFunction(torch.autograd.Function):
         futures = [run_in_background(run_isolated_backward, func, context, *grads)
                    for context, grads in zip(contexts, grad_outputs_per_call)]
         flat_grads_wrt_input = tuple(grad for future in futures for grad in future.result())
-        return None, None, None, None, *flat_grads_wrt_input
+        return (None, None, None, None, *flat_grads_wrt_input)