PHP 8 Support

[GITSKayDomrose]

#35

Update composer requirement and replace deprecated zip functions.

Credit to @michaeldnelson

Edit: Testet with PHP 8.0.0:

$ composer run test
> vendor/bin/phpunit
PHPUnit 9.5.0 by Sebastian Bergmann and contributors.

Runtime:       PHP 8.0.0
Configuration: ./laravel-zipstream/phpunit.xml.dist

....5120+0 records in
5120+0 records out
5368709120 bytes transferred in 1.642410 secs (3268799976 bytes/sec)
.............................5120+0 records in
5120+0 records out
5368709120 bytes transferred in 1.621767 secs (3310407089 bytes/sec)
1024+0 records in
1024+0 records out
1073741824 bytes transferred in 0.346066 secs (3102708241 bytes/sec)
.                                34 / 34 (100%)

Time: 00:28.647, Memory: 20.00 MB

OK (34 tests, 76 assertions)