Small fix to NumberPlane construction

[Solara570]

Due to move_to method, NumberPlane only works fine when the numberplane is symmetric about its center, which makes it infeasible to generate asymmetric grid, for instance, the first quadrant.

The fix is simple: replacing move_to with shift. Here's an example to test if it works.

class TestNumberplaneFix(Scene):
    def construct(self):
        self.add(NumberPlane(x_min=0, y_min=0))
        self.wait()