viewer small bug

[oUp2Uo]

Hi, I saw the latest commit add RongLiu-Leo's viewer.
Thanks for the great work!

And I have a simple test and found small bug:

  File "D:\workspace\2d-gaussian-splatting\view.py", line 50, in <module>
    view(lp.extract(args), pp.extract(args), args.iteration)
  File "D:\workspace\2d-gaussian-splatting\view.py", line 33, in view
    raise e
  File "D:\workspace\2d-gaussian-splatting\view.py", line 25, in view
    net_image = render_net_image(render_pkg, dataset.render_items, render_mode, custom_cam)
  File "D:\workspace\2d-gaussian-splatting\utils\image_utils.py", line 60, in render_net_image
    net_image = colormap(net_image)
  File "D:\workspace\2d-gaussian-splatting\utils\image_utils.py", line 35, in colormap
    colors = torch.tensor(plt.cm.get_cmap(cmap).colors).to(map.device)
AttributeError: module 'matplotlib.cm' has no attribute 'get_cmap'

And the viewer will be freezed after print this.