Require Poison outside tests

[jayjun]

If no serializers are set, OAuth2.Serializer defaults to using Poison.

# mix.exs
def application do
  [applications: [:logger, :hackney],
   env: [serializers: %{"application/json" => Poison}]]
end

This makes Poison a required runtime dependency.

I bumped into this issue after replacing Poison with Jason and running mix deps.clean --unused. Without the explicit requirement, Poison is removed even when code relies on it.

[scrogson]

Hi @jayjun I'm currently working on getting #92 merged and a new release. Serializer registration will no longer be automatic but need to be explicitly registered in the client struct instance.

[scrogson]

To get around the issue you are experiencing here (in the current version), you'll just need to override the defaults with:

config :oauth2,
  serializers: %{"application/json" => Jason}