Fix unused variables warning

Author: axelson

lib/scenic/view_port.ex

@@ -420,7 +420,7 @@ defmodule Scenic.ViewPort do
     GenServer.call(pid, {:set_root, scene, args})
   end
 
-  def set_root(_, %Scene{} = scene, _) do
+  def set_root(_, %Scene{}, _) do
     raise "You must pass the module that represents the scene you want to switch to here, not a `%Scenic.Scene{}`"
   end