Fix Elixir 1.14 warnings

[wpiekutowski]

This PR fixes all warnings emitted by Elixir 1.14.5 (Erlang 25). Probably should be squashed during merge.

warning: use Mix.Config is deprecated. Use the Config module instead
  config/config.exs:1

warning: :hackney_request.encode_form/1 defined in application :hackney is used by the current application but the current application does not depend on :hackney. To fix this, you must do one of:

  1. If :hackney is part of Erlang/Elixir, you must include it under :extra_applications inside "def application" in your mix.exs

  2. If :hackney is a dependency, make sure it is listed under "def deps" in your mix.exs

  3. In case you don't want to add a requirement to :hackney, you may optionally skip this warning by adding [xref: [exclude: [:hackney_request]]] to your "def project" in mix.exs

  lib/exvcr/adapter/hackney/converter.ex:104: ExVCR.Adapter.Hackney.Converter.parse_request_body/1

[barttenbrinke]

warning: :hackney_request.encode_form/1 defined in application :hackney is used by the current application but the current application does not depend on :hackney. To fix this, you must do one of:

  1. If :hackney is part of Erlang/Elixir, you must include it under :extra_applications inside "def application" in your mix.exs

  2. If :hackney is a dependency, make sure it is listed under "def deps" in your mix.exs

  3. In case you don't want to add a requirement to :hackney, you may optionally skip this warning by adding [xref: [exclude: [:hackney_request]]] to your "def project" in mix.exs

  lib/exvcr/adapter/hackney/converter.ex:104: ExVCR.Adapter.Hackney.Converter.parse_request_body/1

This still needs to be done, right?

[coveralls]

coverage: 92.391% (+2.3%) from 90.062% when pulling 469651ad330872aa9029bf42b6b0f5c77ce88d62 on amberbit:fix/elixir-1-14-warnings into 93cb91a193f222748cd0b7e18f5012d95729e6d4 on parroty:master.

[wpiekutowski]

@barttenbrinke @parroty Both warnings are taken care of. PR is ready for review.

[parroty]

Thank you!