[JavaScript] common

修正createElement。
===
var common = {};
common.createElement = function (tag, attributes, parent) {
    var element = document.createElement(tag);
    for (var key in attributes) {
        element.setAttribute(key, attributes[key]);
    }
    if (parent !== undefined) {
        parent.appendChild(element);
    }
    return element;
};
window.common = common;
===.