Why Deplot3d does not work in Maple 2016?

For example, 

with(DEtools);

DEplot3d({diff(y(x), x) = y(x)-z(x), diff(z(x), x) = z(x)-2*y(x)}, {y(x), z(x)}, x = 0 .. 3, [[y(0) = 1.638, z(0) = 2.31]], y = 0 .. 2, z = -4 .. 4, scene = [x, z(x), y(x)], linecolor = COLOR(HUE, .5));

There is nothing shown in Maple 2016.