See 2014 [https://seld.be/notes/my-view-of-php-version-adoption], 2015
[https://seld.be/notes/php-versions-stats-2015-edition], 2016.1
[https://seld.be/notes/php-versions-stats-2016-1-edition], 2016.2
[https://seld.be/notes/php-versions-stats-2016-2-edition], 2017.1
[https://seld.be/notes/php-versions-stats-2017-1-edition], 2017.2
[https://seld.be/notes/php-versions-stats-2017-2-edition], 2018.1
[https://seld.be/notes/php-versions-stats-2018-1-edition], 2018.2