PyG 2.0.1

This is a minor release, bringing some emergency fixes to PyG 2.0.

Bugfixes

• Fixed a bug in loader.DataLoader that raised a PicklingError for num_workers > 0 (thanks to @r-echeveste, @arglog and @RishabhPandit-00)
• Fixed a bug in the creation of data.Batch objects in case customized data.Data objects expect non-default arguments (thanks to @Emiyalzn)
• Fixed a bug in which SparseTensor attributes could not be batched along single dimensions (thanks to @rubenwiersma)