httpotion retired

[wkirschbaum]

When running mix deps.get, the following warning pops up:

 httpotion 3.2.0 RETIRED!
    (deprecated) Not really maintained, please check out Tesla

but think instead of Tesla perhaps we should use Finch.

[wkirschbaum]

related: dashbitco/broadway_sqs#73

[bernardd]

I don't really have a strong opinion on the preferred alternative, so I'd be happy with a PR for either (or httpoison, which I mention merely because it has a pleasingly similar name, and not because I have any knowledge or opinion of the relative technical merits). Note, though, that the selection of httpotion is only for testing, and the idea is that, as with the JSON library, you should be able to plug in any backend you like. So as long as that remains the case, I'm pretty much happy with whatever.

[wkirschbaum]

@bernardd just as an idea and should not be a breaking change: #960

This will also allow Finch to be used as Req is built on top of Finch.