参考： https://segmentfault.com/a/1190000009461832
步骤：
function shellSort(arr) {
var len = arr.length,
temp,
gap = 1;
while(gap < len/3) { //动态定义间隔序列
gap = gap*3+1;
}
for (gap; gap > 0; gap = Math.floor(gap/3)) {
for (var i = gap; i < len; i++) {
temp = arr[i];
for (var j = i-gap; j >= 0 && arr[j] > temp; j -= gap) {
arr[j+gap] = arr[j];
}
arr[j+gap] = temp;
}
}
return arr;
}
