af::plot function

Hi,

I am trying to use "af::plot" to plot a vector, but it does not display any plots. Here is a sample code:

```
    int width = 2540;
    af::array Y = af::constant<float>(62280.0, (width), f32);
    af::array X = af::seq((double)1, (double)width);

    af::Window plotWin("plot");
    while (!plotWin.close())
        plotWin.plot(X, Y);
```

I would appreciate any help! Thanks!
