Fix some more upgrade issues

lib/chess/repo.ex

@@ -1,3 +1,3 @@
 defmodule Chess.Repo do
-  use Ecto.Repo, otp_app: :chess
+  use Ecto.Repo, otp_app: :chess, adapter: Ecto.Adapters.Postgres
 end

lib/chess/store/game.ex

@@ -2,7 +2,6 @@ defmodule Chess.Store.Game do
   @moduledoc false
 
   use Ecto.Schema
-  use Timex.Ecto.Timestamps
 
   import Ecto.Changeset
   import Ecto.Query

lib/chess/store/move.ex

@@ -2,7 +2,6 @@ defmodule Chess.Store.Move do
   @moduledoc false
 
   use Ecto.Schema
-  use Timex.Ecto.Timestamps
 
   import Ecto.Changeset
 

lib/chess_web/endpoint.ex

@@ -33,7 +33,7 @@ defmodule ChessWeb.Endpoint do
   plug Plug.Parsers,
     parsers: [:urlencoded, :multipart, :json],
     pass: ["*/*"],
-    json_decoder: Poison
+    json_decoder: Jason
 
   plug Plug.MethodOverride
   plug Plug.Head