bootstrap 4 pull-right无效

/**********************************************************************
 *                   bootstrap 4 pull-right无效
 * 说明：
 *     在测试bootstrap的时候发现pull-right无效，原来是已经换成了float-right。
 *
 *                                2018-4-25 深圳 宝安西乡 曾剑锋
 *********************************************************************/

一、参考文档：
    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、解决办法：
    The classes are currently float-right float-sm-right etc.