[Bug Report] Popover with hover trigger only stays open while tap is sustained on IE11

### Element UI version
2.15.0

### OS/Browsers version
Windows 10 / Internet Explorer 11

### Vue version
2.6.12

### Reproduction Link
https://jsfiddle.net/d10fyL46/

### Steps to reproduce
Using a touchscreen device, tap on any popover with a hover trigger using IE11 (this is visible on https://element.eleme.io/#/en-US/component/popover#basic-usage too - which is much easier to access than trying to use JSFiddle / CodePen on IE11!)

### What is Expected?
Popover remains after tapping, until tapping elsewhere

### What is actually happening?
Popover only visible while tap is held - on releasing, the popover disappears