Problem

If you ever get an error similar to this while creating a release with
exrm:

Errors generating release
          Duplicated modules:
        'Elixir.Poison.Encoder.Ecto.Time' specified in ecto and phoenix_ecto
        'Elixir.Poison.Encoder.Ecto.DateTime' specified in ecto and phoenix_ecto
        'Elixir.Poison.Encoder.Ecto.Date' specified in ecto and phoenix_ecto
        'Elixir.Poison.Encoder.Decimal' specified in ecto and phoenix_ecto

Solution

Simply delete the `mix.lock` file and get the dependencies again `mix deps.get`.