[Bug Report] a bug of el-select

### Element UI version
2.14.1

### OS/Browsers version
win7 chrome

### Vue version
2.6.12

### Reproduction Link
https://codepen.io/losedguest/pen/vYXroEw

### Steps to reproduce
filterable multiple 時設置defaultFirstOption沒有用
比如輸入 "北" ,回車

### What is Expected?
輸入 "北",回車后,第一項應該被選中,然後關閉下拉

### What is actually happening?
回車沒有反應
原因是compositionend執行時,this.query的值還沒來得及變化