Update js/cufon.js

[Devolv]

Update padding top when Device Ratio is greater than 1, padding is also multiplied by PixelRatio to prevent insufficient padding.

[Devolv]

This is in relation to previous issue: #222

With Retina devices - padding within the canvas elements are incorrect. Padding unit used within the Canvas element is pixels, and when using the device-pixel-ratio=2 doubles the padding as well, but this creates too much padding on the Retina devices. Text height alignment is off as well, so vertically centering Cufon text on a header consistently would be impossible for both Retina and Non-Retina devices. Characters such as "g", "j" etc are also being clipped off the edge of the canvas element.

[Devolv]

My patch seems to work a lot better, but there is still bottom padding that I could not remove.