Update for PHP 8.1

[repat]

Hi,

v.3.0.0 allows for PHP 8.1 (^8.0) and my preliminary testing (FCM notification for my phone) confirms it's working. However, ^3.1 goes back to PHP ~8.0, not sure why? Can you look into officially supporting PHP 8.1?

I know PHP 8.1 has just been released end of last week but I just wanted to leave an issue for this :-)

Thanks!

[jeromegamez]

PHP 8.1 wasn't released at the time, and I'm often switching between not wanting to block people testing with yet-unreleased PHP versions and only supporting what I can actually confidently support 😅.

PHP 8.1 support was re-added with #110, I just forgot to release it, which is now done with 3.3.0 - thank you for the nudge!