KeepRequest middleware

[teamon]

Put request headers and body in opts.
Not sure if this will work, needs to be tested.

defmodule Tesla.Middleware.KeepRequest do
  def call(env, next, _opts) do
    env
    |> Tesla.put_opt(:req_body, env.body)
    |> Tesla.put_opt(:req_headers, env.header)
    |> Tesla.run(next)
  end
end