title: Elixir Plug Cowboy not using port 80
body: <p>I have a Router plug</p>
  
  <pre><code>defmodule Rest do
    use Plug.Router
    import Plug.Conn
  
    plug :match
    plug :dispatch
  
    get "/hello" do
      send_resp(conn, 200, "Hello, world!")
    end
  
    match _ do
      send_resp(conn, 404, "oops")
    end
  
    def start do
      Plug.Adapters.Cowboy.http Rest, [], port: 80
    end
  
    def stop do
      Plug.Adapters.Cowboy.shutdown Rest.HTTP
    end
  end
  </code></pre>
  
  <p>However, when calling Rest.start I get</p>
  
  <pre><code>{:error,
   {{:shutdown,
     {:failed_to_start_child, :ranch_acceptors_sup,
      {{:badmatch, {:error, :eacces}},
       [{:ranch_acceptors_sup, :init, 1,
         [file: 'src/ranch_acceptors_sup.erl', line: 30]},
        {:supervisor, :init, 1, [file: 'supervisor.erl', line: 243]},
        {:gen_server, :init_it, 6, [file: 'gen_server.erl', line: 306]},
        {:proc_lib, :init_p_do_apply, 3, [file: 'proc_lib.erl', line: 239]}]}}},
    {:child, :undefined, {:ranch_listener_sup, Rest.HTTP},
     {:ranch_listener_sup, :start_link,
      [Rest.HTTP, 100, :ranch_tcp, [port: 200], :cowboy_protocol,
       [env: [dispatch: [{:_, [],
           [{:_, [], Plug.Adapters.Cowboy.Handler, {Rest, []}}]}]],
        compress: false]]}, :permanent, :infinity, :supervisor,
     [:ranch_listener_sup]}}}
  </code></pre>
  
  <p>If I remove the port: 80, there is no problem calling Rest.start, and the server listens on port 4000.</p>
  
  <p>I am using Elixir v0.15.0.</p>