update to 1.3.1

This version will properly use /var/db/privatebin
instead of %%PREFIX%%/www/privatebin

While here, fix some portlint issues

• trailing spaces in pkg-descr
• move USES= up in Makefile

PR: 242838
Submitted by: dvl@FreeBSD.org
Approved by: se@FreeBSD.org (maintainer timeout - 25 days)