add support for zoom

[dingyaguang117]

when vue-slicksort in a element which has zoom attribute, the offset is wrong

[ChrisRoss5]

It is a complicated style, which many libraries don't support. It is Non-standard [MDN]. Probably the only solution relies on getComputedStyle(elWithZoom).zoom which would require knowing in advance which element(s) have zoom applied + the performance overhead of getComputedStyle, which is actually quite a lot.