Function setTranslate

src/picker/scroll.js:35–40

($target, diff)

 * set translate
 */
const setTranslate = ($target, diff) => {
    return $target.css({
        '-webkit-transform': `translate3d(0, ${diff}px, 0)`,
        'transform': `translate3d(0, ${diff}px, 0)`
    });
};

/**
 * @desc get index of middle item