www/wt3: Update to 3.6.1

Changelog:

• https://www.webtoolkit.eu/wt/wt3/doc/reference/html/Releasenotes.html

PR: 245990
Submitted by: Mohammad S. Babaei (maintainer)
Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D24634