Adapter: Ecto.Adapter.Postgres

Hi i am new to phoenix and elixir and i am trying to make a textbox that insert 1 data into database and have some error :

== Compilation error in file lib/zivot_web/controllers/topic_controller.ex ==
** (KeyError) key :otp_app not found in: []
    (elixir) lib/keyword.ex:389: Keyword.fetch!/2
    lib/ecto/repo/supervisor.ex:62: Ecto.Repo.Supervisor.compile_config/2
    lib/zivot_web/controllers/topic_controller.ex:3: (module)
    (stdlib) erl_eval.erl:680: :erl_eval.do_apply/6
    (elixir) lib/kernel/parallel_compiler.ex:208: anonymous fn/4 in Kernel.ParallelCompiler.sp

repo.ex:

defmodule Zivot.Repo do
  use Ecto.Repo,
    otp_app: :zivot,
    adapter: Ecto.Adapters.Postgres
end

tabela.ex

defmodule Zivot.Tabela do
  use Ecto.Schema
  import Ecto.Changeset


  schema "topics" do
    field :topic, :string

    timestamps()
  end

  @doc false
#  def changeset(struct, params) do
#    struct
#    |> cast(params, [:topic])
#    |> validate_required([:topic])
#  end
end

defmodule ZivotWeb.Tabela do
  use Ecto.Schema
  import Ecto.Changeset
  def changeset(struct, params) do
    struct
    |> cast(params, [:topic])
    |> validate_required([:topic])
  end
end

defmodule ZivotWeb.TopicController do
  use ZivotWeb, :controller
  use Ecto.Repo
  alias Zivot.Tabela

 def new(conn, params) do
    struct = %Tabela{}
    params = %{}
    changeset = ZivotWeb.Tabela.changeset(struct,params)
    render conn, "new.html", changeset: changeset
  end
#  def create(conn, %{"tabela" => topic_params}) do
  #  changeset = ZivotWeb.Tabela.changeset(%Tabela{}, topic_params)
  #  case Repo.insert(changeset) do
  #    {:ok, post} ->
        #conn
      #  |> put_flash(:info, "Topic created")
      #  |> redirect(to: Routes.topic_path(conn, :index))
  #    {:error, changeset} ->
  #      render conn, "new.html", changeset: changeset
  #  end
  #end
end

new.html

<%= form_for @changeset, Routes.topic_path(@conn, :create), fn f -> %>
<%= text_input f, :topic %>
<%= submit "Save Topic" %>
<% end %>