[ios]Fixed the problem that the list was not automatically restored when the loading tag was pulled up under certain conditions

[yuditxj]

Fix the problem that when the list is under one piece of data, the loading label will be displayed by default in the drop-down refresh list

复现条件:
list标签数据不超过一屏时，同时存在refresh和loading标签，若上拉加载列表(没有更多数据)，仅仅快速切换(100ms)loading标签的display属性由true为false，发现列表位置不会自动还原

原因:
Probably setContentOffset: has higher priority than setContentOffset:animated:

方案:
参考refresh标签的说明，针对displayState字段不同值，调整设置setContentOffset方式

Brief Description of the PR

Checklist

• Demo:http://dotwe.org/vue/ab6efd1b38c9beaec2cae3a99e3ecf79

Refreshing ... {{num}} Loading ... <script> const modal = weex.requireModule('modal') export default { data () { return { refreshing: false, loadinging: false, lists: [1, 2, 3, 4, 5] } }, methods: { onrefresh (event) { modal.toast({ message: 'Refreshing', duration: 1 }) this.refreshing = true setTimeout(() => { this.refreshing = false }, 2000) }, onpullingdown (event) { console.log("dy: " + event.dy) console.log("pullingDistance: " + event.pullingDistance) console.log("viewHeight: " + event.viewHeight) console.log("type: " + event.type) }, onloading (event) { modal.toast({ message: 'Loading', duration: 1 }) this.loadinging = true setTimeout(() => { this.loadinging = false }, 2000) }, } } </script> <style scoped> .refresh { width: 750px; height: 180px; background-color: #333; display: -ms-flex; display: -webkit-flex; display: flex; -ms-flex-align: center; -webkit-align-items: center; -webkit-box-align: center; align-items: center; } .indicator-text { color: #EEE; font-size: 42px; text-align: center; } .indicator { margin-top: 16px; height: 40px; width: 40px; color: blue; } .panel { width: 600px; height: 250px; margin-left: 75px; margin-top: 35px; margin-bottom: 35px; flex-direction: column; justify-content: center; border-width: 2px; border-style: solid; border-color: #DDDDDD; background-color: #F5F5F5; } .text { font-size: 50px; text-align: center; color: #41B883; } </style>

• Documentation:

[Txink]

麻烦合并一下PR，还有就是能提供一个验证demo么

[yuditxj]

麻烦合并一下PR，还有就是能提供一个验证demo么
demo地址：
http://dotwe.org/vue/ab6efd1b38c9beaec2cae3a99e3ecf79

[Txink]

LGTM