Spacing does not size horizontal gesture

[mees-brenzie]

Hi!

First of all, thank you for this library!

I noticed, when you change the spacing attribute, the horizontal sliding gesture does not scale with it. An example shown here:

(scaling set to 30 and size 36)

Hope you can review this issue!
All the best

[ishmelev23]

@thangmam @p30arena guys, just replace the index calculation with the next block:

var i = (_pos.dx + widget.spacing / 2) / (widget.size + widget.spacing);
var newRating = widget.allowHalfRating ? i : i.ceilToDouble();