PHP 7.4 has introduced a deprecation warning about `implode(list, glue)`:
> implode(): Passing glue string after array is deprecated. Swap the parameters.
See:
- <https://github.com/phacility/phabricator/pull/848>
- <https://discourse.phabricator-community.org/t/libphutil-exception-when-using-with-newer-php-deprecated-use-of-implode/3159>