Opacity value can be 1.0 but cannot be 1

[dorukozturk]

Something minor but can be fixed easily.

Works:

M.add_layer(rd[1, 2, 3], interval=(0,1), gamma=2, opacity=1.0)

Does not work:

M.add_layer(rd[1, 2, 3], interval=(0,1), gamma=2, opacity=1)