PF4 dropdowns cannot be closed on iOS/Mobile Safari

[rhamilto]

Following on to #1113, dropdowns cannot be closed by clicking the dropdown toggle or the non-clickable negative space elsewhere on the page in iOS/Mobile Safari . The only way to close a dropdown in iOS/Mobile Safari is to click one of the dropdown menu items or another clickable item elsewhere on the page.

[jgiardino]

I think this issue is a duplicate of #984, but let me know if not.