Update request logic to handle error reasons in keyword lists

[maciejgryka]

Fixes #1005 by updating request.ex to also handle errors in the form of [reason: reason] in addition to %{reason: reason}.

[x] Run mix format using a recent version of Elixir
[x] Run mix dialyzer to make sure the typing is correct
[x] Run mix test to ensure no tests have broken (also please make sure you've added tests for your particular change, where appropriate).

[bernardd]

Great, thanks very much @maciejgryka. Apologies for the delay in getting to this.