Dependency on php version 5.4

[bramley]

An earlier pull request used the short array syntax assuming that php version 5.4 or later is being used. https://github.com/phpList/phplist3/pull/543/files#diff-c24d5bdfa2b25ebe4461a8063f6b83a8R910

But it is still the case that phplist allows php 5.3.3

    if (version_compare(PHP_VERSION, '5.3.3', '<') && WARN_ABOUT_PHP_SETTINGS) {
        Error(s('Your PHP version is out of date. phpList requires PHP version 5.3.3 or higher.'));
    }

That change makes the subscribe/preferences page fail for php < 5.4, see https://discuss.phplist.org/t/subscriber-update-preferences-screen-is-blank/5483

[michield]

@samtuke I'm not sure that should be fixed? PHP5.3 should really be retired.

In fact, PHP5.6 is out of support since December 2018, so maybe ẁe should do so as well. I know some Centos fanatics want to keep it, but that's their problem.

[ryancwalsh]

It looks like @bramley was recommending to update the part that says version_compare(PHP_VERSION, '5.3.3', '<').