[Bug Report] The filter attribute in el-select is added, and the arrow cannot be retrieved by clicking the arrow; After the filter property in el-select is added, click the arrow to collapse

### Element UI version
2.7.2

### OS/Browsers version
windows/mac

### Vue version
2.6.10

### Reproduction Link
https://codepen.io/anon/pen/qwMaGX

### Steps to reproduce
el-select 中 添加 filterable 属性后，点击箭头无法收起，从@2.3.4 后的都变成 展开后无法收起了 ；
After adding the filterable attribute to el-select, clicking the arrow will not be able to close it, and it will not be retracted after the expansion from @2.3.4.

### What is Expected?
el-select 中 添加 filterable 属性后，点击右边的箭头可以切换收起，或展开；
After adding the filterable property to el-select, click the arrow on the right to toggle the collapse, or expand.

### What is actually happening?
实际目前的行为，el-select 加入filterable 后 点击右侧的 箭头无法 将展开的数据 收起，点击无效;
Actual actual behavior, after el-select is added to filterable, click the arrow on the right to disable the expanded data, click invalid.