Update the Guzzle dependency to 7.0

[JulienMalbrecq]

I'm trying to use php-google-maps-distance-matrix in a Laravel 8 app. Laravel requires Guzzle ^7.0.1. The Guzzle interface does not seem to change between versions 6 & 7, hence it should be safe to simple update the dependency requirement. Could you please update the depencies ?

[Jono20201]

@JulienMalbrecq We no longer use this library internally, can you make a PR to achieve this?

[ziarv]

any update here ?

[Jono20201]

Should be resolved by #10