fix: check for correct claim in JWT in auth_required plug

lib/localiser/web/plugs/auth_required.ex

@@ -9,7 +9,7 @@ defmodule Localiser.Web.Plugs.AuthRequired do
     with ["Bearer " <> token] <- get_req_header(conn, "authorization"),
          {:ok, claims} <- Token.verify_token(token) do
       assign(conn, :current_user, %{
-        user_id:  claims["user_id"],
+        user_id:  claims["sub"],
         username: claims["username"],
         is_admin: claims["is_admin"]
       })