PHP 7.2 support, drop HHVM - update Travis CI configuration

[michalbundyra]

• [x] drops HHVM
• [x] adds PHP 7.2
• [x] adds missing cs checks
• [x] removes docs build (handled now by zendframework/zf-bot)
• [x] removes IRC notifications (no longer used)
• [x] sets composer column width to 120 chars
• [x] updated php-coveralls (version 2 has php-coveralls script)

Please note that develop !== master right now: develop is 36 commits ahead master https://github.com/zendframework/zend-navigation/compare/develop

[weierophinney]

Thanks, @webimpress!