Fix/update jquery atwho rails

there is a new jquery-atwho-rails version out there which renames their js-include-files.

People seem to stumble over this change which is why I want to provide an update to the latest version.

see: https://www.openproject.org/work_packages/5079
and https://www.openproject.org/topics/693?board_id=9

Changelog Entry:
    * `#5979` Update to current version of jquery.atwho