Issue description

We identified a behavior change after promoted Anchorjs from v4.2.2 to v4.3.0.

We are using visible: touch as anchor options. For v4.2.2, the anchor is hover on page of Windows10, after promoted to v4.3.0, the anchor is always there instead of hover.

Here are sample pages to help understand the issue:
v4.2.2 page(hover): https://kleisauke.github.io/net-vips-tests/api/NetVips.html
v4.3.0 page(always): https://kleisauke.github.io/net-vips/api/NetVips.html

Operating System: Windows

AnchorJs version: 4.3.0

Expected Behavior:
AnchorJS links only become visible when hovering over the headings like before for Windows when visible is touch.

Actual Behavior:
AnchorJS links are always visible for Windows when visible is touch.

Note:
This behavior change seems related to the newly added condition window.TouchEvent in function isTouchDevice() with this commit

isTouchDevice() for v4.3.0:
this.isTouchDevice=function(){return Boolean("ontouchstart"in window||window.TouchEvent||window.DocumentTouch&&document instanceof DocumentTouch)}

isTouchDevice() for v4.2.2:
,this.isTouchDevice=function(){return!!("ontouchstart"in window||window.DocumentTouch&&document instanceof DocumentTouch)}