Update HTTPoison functions
In order to remain compatible with newer (as of about 1.4.0) versions of HTTPoison, update override functions in Forcex.Api.Http and in Forcex.Bulk. These functions now treat headers as a keyword list, which requires changes to the function logic.
Closes #52
While my ultimate goal is to bring the library up to date with the latest versions for elixir and dependencies, I wanted to start with a green slate by fixing the outstanding dialyzer failures with as few changes as possible.
I have a branch that brings all deps up to date and updates elixir/OTP to 1.13 / 24: https://github.com/fastjames/forcex/tree/elixir_113 . Once this PR has been merged I'll rebase that branch and open a PR on it.
@jeffweiss Any chance we could get this one merged? This keeps anyone using forcex tied to a version of httpoison that's 5 years old.