Upgrade Guzzle

[danwdart]

I think supported versions of Guzzle are 6.x (maybe 5.x) but this library requires ~3 which means it conflicts with anything else using more up-to-date versions of Guzzle.

Not sure what's involved in changing to that of later versions of Guzzle - but probably not much more than updating composer (I'm guessing?)

Can make PR for that but couldn't verify everything would work again.

[fabre-thibaud]

I think you'd also need to update the library to use Guzzle's new API, which may or may not be a lot of work (I don't know the library well enough yet to have an answer). If you're feeling up to it, you can go ahead and submit a P/R (we have unit tests to ensure that everything still works)

[wojtow]

A PR was submitted that brings Guzzle (and other dependencies) up to date. If not yet merged, see https://github.com/wojtow/RabbitMQ-Management-API-Client "circa2019" branch