www/fabio: Update to 1.5.14

The update from 1.5.9 to 1.5.14 brings many bug fixes, enhancements and some new features[1].

[1] https://github.com/fabiolb/fabio/releases/

PR: 249219
Submitted by: Gian-Simon Purkert <gspurki@gmail.com>
Approved by: tcberner (mentor), Scott Larson (maintainer timeout)
Differential Revision: https://reviews.freebsd.org/D27105