Updated Guzzle to ^7.0.1 for Laravel 8 compatibility

[fakingfantastic]

Hey @adamwathan 👋

Just as it says on the tin: I updated the dependency for Guzzle. Ran the tests, and they are all green.

Any questions, let me know - hope this helps 👍

[fakingfantastic]

Linking to Issue #90

[fakingfantastic]

Closing as @adamwathan pointed out Laravel 8 has a more feature-rich version of Zttp called Http: https://twitter.com/adamwathan/status/1305644837698449408

[beNjiox]

I think this is still something that could be great!

I rely on a non-laravel package using ZTTP. Can't get to Laravel8 upgrade because it won't let me since this package doesn't support the new guzzle version.
Ended up using a forked version, so I think that would be awesome to get this merged while everyone is moving from it :)

Cheers!