text: Title: Unsupported gzip encoding for NRRD reader
  Body: I would like to open a volume and slice it with vedo using code example provided by Marco:
  ```
  from vedo import load, show
  from vedo.applications import Slicer
  
  file_path = './average_template_100.nrrd'
  vol = load(file_path)
  
  plt = Slicer(vol, bg='white', bg2='lightblue', useSlider3D=False)
  plt.show()
  ```
  
  but the code fails with this error:
  ```
  2020-12-01 22:41:59.342 (   1.042s) [          905B63]      vtkNrrdReader.cxx:395    ERR| vtkNrrdReader (0x7fb2b8469d40): Unsupported encoding: gzip
  2020-12-01 22:41:59.342 (   1.043s) [          905B63]       vtkExecutive.cxx:753    ERR| vtkCompositeDataPipeline (0x7fb2b8445e70): Algorithm vtkNrrdReader(0x7fb2b8469d40) returned failure for request: vtkInformation (0x7fb2b55e4960)
    Debug: Off
    Modified Time: 159
    Reference Count: 1
    Registered Events: (none)
    Request: REQUEST_INFORMATION
    ALGORITHM_AFTER_FORWARD: 1
    FORWARD_DIRECTION: 0
  
  
  Slicer tool
  2020-12-01 22:42:00.220 (   1.920s) [          905B63]vtkSmartVolumeMapper.cx:271    ERR| vtkSmartVolumeMapper (0x7fb2b8469fa0): Could not find the requested vtkDataArray! 0, 0, -1,
  2020-12-01 22:42:00.249 (   1.949s) [          905B63]vtkSmartVolumeMapper.cx:271    ERR| vtkSmartVolumeMapper (0x7fb2b8469fa0): Could not find the requested vtkDataArray! 0, 0, -1,
  ```
  
  I have loaded the same volume within Paraview (VTK) all fine.
  Is it because of an older VTK version or because of how vtkNrrdReader is called? Or something else?