increase the thickness of cube

data/cube_shallow.off

@@ -2,14 +2,14 @@ OFF
 #  cube.off
 #  A cube
 8 12 0
--1 -0.01 -1
-1 -0.01 -1
--1 0.01 -1
-1 0.01 -1
--1 -0.01 1
- 1 -0.01 1
--1 0.01 1
- 1 0.01 1
+-1 -0.1 -1
+1 -0.1 -1
+-1 0.1 -1
+1 0.1 -1
+-1 -0.1 1
+ 1 -0.1 1
+-1 0.1 1
+ 1 0.1 1
 3   0 2 1
 3   2 3 1
 3   1 3 5