[Chore] Review codebase after PHP < 7.1 version drop

After discussion in #157, PR #163 dropped support for PHP < 7.1 from the package.

This is just a reminder that there may be code simplifications and modernizations which can be made now PHP < 7.1 no longer needs to be supported.

A cursory review of the codebase to execute this would be a worthwhile effort to improve the maintainability of the code for the future.