bootstrap 4 pull-right無效

/**********************************************************************
 *                   bootstrap 4 pull-right無效
 * 說明：
 *     在測試bootstrap的時候發現pull-right無效，原來是已經換成了float-right。
 *
 *                                2018-4-25 深圳 寶安西鄉 曾劍鋒
 *********************************************************************/

一、參考文檔：
    1. What happened to the .pull-left and .pull-right classes in Bootstrap 4?
        https://stackoverflow.com/questions/39655110/what-happened-to-the-pull-left-and-pull-right-classes-in-bootstrap-4
    2. pull-right replacement in bootstrap 4 does not work
        https://stackoverflow.com/questions/46221635/pull-right-replacement-in-bootstrap-4-does-not-work

二、解決辦法：
    The classes are currently float-right float-sm-right etc.