fixed rounding cellWidth twice

[LomoSoftGmbH]

When using more cols > 12, in my case 40, the doubled rounding forces an unprecise dragging/dropping of widgets

[coveralls]

Coverage decreased (-43.9%) to 28.4% when pulling 0a6bd2c on LomoSoft:cellWidth into 99653bd on troolee:master.

[troolee]

Hi @LomoSoftGmbH,

thanks for PR, but I didn't get it. Code is the same, you just moved Math.ceil inside the call. Did you want to get smth like:

Math.ceil(cellWidth * (node.minWidth || 1))
..................^^^....................^^^