Update vtkm

@berkgeveci @NAThompson Working on finishing up the addition of ADIS as a module of VTK and realized I needed to update the VTK-m version we use. It only required a minor fix (of a type alias that's actually unused in the code). Also updated the docker images, along with adding a update-vtkm.md file so I don't have to worry about forgetting what should be changed when updating (though it is mostly automated now).