[bug report] add a table in dialog. Some data items in the table are changed, and the UI does not respond

### Element UI version
2.3.4

### OS/Browsers version
chrome

### Vue version
2.6.12

### Reproduction Link
https://elementui.github.io/issue-generator/#/zh-CN

### Steps to reproduce

js如下：
情景1：
$this.currentServer.items[0].value = '111' ui不更新

情景2：
$this.currentServer.items[0].name = '111' ui更新

情景3：
$this.currentServer.items[0].value = '111'
$this.currentServer.items[0].name = '111'
两个ui都更新

情景4：
$this.currentServer.items[0].name = '111'
$this.currentServer.items[0].value = '111'
两个ui都更新

### What is Expected?
解决bug

### What is actually happening?
解决bug