Relax adapter deps

[mtarnovan]

Could the deps on mint and httpoison be relaxed a bit to work with mint 1.4 and httpoison 1.8 without overriding?

Thanks

[fireproofsocks]

Or even HTTPoison v2, now that it's out...

[cigzigwon]

I agree. It seems like HTTPoison 1.8 would be a drop-in.