element 时间选择器，显示时间，值为年月日，时分秒

<el-date-picker

          v-model="selectValue"

          style="width:240px"

          class="reset-clear"

          type="daterange"

          :clearable="false"

          unlink-panels

          start-placeholder="开始日期"

          end-placeholder="结束日期"

          value-format="yyyy-MM-dd HH:mm:ss"

          :default-time="['00:00:00', '23:59:59']"

          @change="changeValue"

        />