www/piwik: Update from 3.0.4 to 3.2.0

Changelog: https://piwik.org/changelog/piwik-3-1-0/
Changelog: https://piwik.org/changelog/piwik-3-1-1/
Changelog: https://piwik.org/changelog/piwik-3-2-0/

This update also fixes to XSS security issues. Read changelog
for 3.1.0 for more information.

MFH: 2017Q4