You should probably tweak the plugin to require a lower version of symfony/yaml that is compatible with PHP 7.0. (For example, Craft 3.1+ requires symfony/yaml at ^3.2|^4.0.) Otherwise people get Composer errors when attempting to install the plugin.
Since v2.2.12, The Architect has required
symfony/yaml
at^4.1
(d7f68713eeee4959994548fb35941d74ca72123f).However
symfony/yaml
4.1+ requires PHP 7.1.3 or later, which conflicts with the defaultphp
platform requirement that Craft projects have:https://github.com/craftcms/craft/blob/master/composer.json#L33
You should probably tweak the plugin to require a lower version of
symfony/yaml
that is compatible with PHP 7.0. (For example, Craft 3.1+ requiressymfony/yaml
at^3.2|^4.0
.) Otherwise people get Composer errors when attempting to install the plugin.