jQuery 1.x branch supports IE6~8, but since ZK 8.5 we only support IE9.
So no need to stick on 1.x.

There are some reasons to upgrade:

• https://github.com/jquery/jquery/issues/2432 (not in 1.x, needs to patch by self. We have this patch in ZK)
• https://blog.jquery.com/2020/04/10/jquery-3-5-0-released/ (jQuery.htmlPrefilter security fix)
• Smaller size, better performance