Add extra type cast to String before call split()

[MinhThienDX]

Fix bug when call split() on number
Similar to this PR #74 but he changed the minified version

[pduey]

Instead of calling data("chained") and casting to String, per the jquery docs, we could call attr("data-chained") instead, and instead of coercing strings into numbers, the String type will be preserved.

I've done that on my own branch and it works.

// var data = $(this).data("chained");
var data = $(this).attr("data-chained");