Support Hackney 3.x

[tomekowal]

Hi!

Hackney 2.x came out https://github.com/benoitc/hackney/blob/master/NEWS.md

In the migration guide it states:

Simple requests: No changes needed

Judging from the fact that Streaming with Hackney PR is not merged, I assume that it should be enough to change {:hackney, "~> 1.21", optional: true} to {:hackney, "~> 1.21 or ~> 2.0", optional: true}. If that is the case, I can make the PR. If I am missing something, please, let me know.

[yordis]

@tomekowal please take the lead if you can, we must keep backward compatible. I am gonna be off for 2 weeks so at least that long until I come back to this issue.

I can support with code review, CI, and limited experience with hackney internals

[tomekowal]

Thanks! I was wrong about hackney streaming support. I started a PR #824 but got blocked on API change that I am not sure was intentional in hackney, so I opened an issue benoitc/hackney#821

[tomekowal]

It seems that 2.x had some unintended braking changes, so there is a new major release 3.x. I've edited the ticket name. I should be able to resume work on updating straight to 3.x during the weekend :)

I am going to specify {:hackney, "~> 1.21 or ~> 3.0", optional: true} to completely skip the support for 2.x and only support 1.x and 3.x

[tomekowal]

I've found another issue which I am not sure is accidental breaking change, so I'll wait for the response
benoitc/hackney#823