[Bug Report] Fixed column height is not adaptive

### Element UI version
2.4.4

### OS/Browsers version
Win10 / Google Chrome 67.0.3396.99（正式版本） （64 位）

### Vue version
2.5.16

### Reproduction Link
[https://jsfiddle.net/mmx38qxw/3959/](https://jsfiddle.net/mmx38qxw/3959/)

### Steps to reproduce
使用el-table表格控件, 指定第一列和最后一列为fixed, 除此之外中间某一列使用文件上传插件.
Use the el-table form control to specify the first column and the last column to be fixed. In addition, a column in the middle uses a file upload plug-in.

### What is Expected?
单元格内容导致行高度变化时, 固定列也需要同时匹配变化
When the cell content changes the height of the row, the fixed column also needs to match at the same time.

### What is actually happening?
单元格内容导致行高度变化时, 固定列并没有自适应, 导致固定列行高错位
When the cell content changes the height of the row, the fixed column is not adaptive, leading to the high dislocation of the fixed column row.