www/validator: Change p5-CGI.pm dependency to p5-CGI

Using p5-CGI rather than p5-CGI.pm is more convenient for many people
because many www ports depends on p5-CGI and it conflicts with p5-CGI.pm.
Also pet portlint.

PR: 227653
Submitted by: cyberbotx@cyberbotx.com (maintainer)
Approved by: pi (mentor)
Differential Revision: https://reviews.freebsd.org/D15414