www/foswiki: update 2.1.3 -> 2.1.6

PR: 227796
Requested by: Doug Sampson <dougs@dawnsign.com>
Submitted by: pi
Approved by: Chris Hutchinson <portmaster@bsdforge.com> (maintainer)
Relnotes: http://foswiki.org/System/ReleaseNotes02x01
Security: CVE-2018-7446