[Bug Report] TableColumn：the filtered-value property cannot reset the filtered value

### Element UI version
2.13.0

### OS/Browsers version
MacOS10.15.2

### Vue version
2.6.11

### Reproduction Link
https://jsfiddle.net/hyg3jwmu/

### Steps to reproduce
1. initialize a el-table，and set filters, filtered-value in el-table-column. In the case, the initial filtered-value is ['2016-05-01']
2. change the filtered value in a function like mouted to ['2016-05-01', '2016-05-02']

### What is Expected?
The expected selected value in el-table-column header is ['2016-05-01', '2016-05-02']

### What is actually happening?
The expected selected value in el-table-column header is ['2016-05-01']