Move to blessed fork of box for building phars

[mwgamble]

There is a new version of box released by the humbug organisation:

https://github.com/humbug/box

It offers significant improvements over the old version, including speed, and has removed various deprecated dependencies:

https://github.com/humbug/box/blob/master/UPGRADE.md

It would be great if this project could be updated to make use of it.

[jrfnl]

In the mean time, it has been: https://github.com/php-parallel-lint/PHP-Parallel-Lint/pull/70

[mwgamble]

:heart: Thank you!

You're an unsung hero of the PHP ecosystem.

[jrfnl]

@mwgamble Thanks Matthew! 😊