Duration类型

Duration - 无创建接口，会在Integer类型数据调用日期/时间类型数据时返回

定义Duration：<Integer>.years;

                        <Integer>.months;

                        <Integer>.days;

                       <Integer>.hours;

                       <Integer>.minutes;

例：

>     Date date = "2019-01-01"

>     date = date + 1.months //返回：2019-02-01