fix closing window

src/backends/glvisualize.jl

@@ -159,12 +159,12 @@ function create_window(plt::Plot{GLVisualizeBackend}, visible)
     # make sure we have any screen open
     if isempty(GLVisualize.get_screens())
         # create a fresh, new screen
-        screen = GLVisualize.glscreen(
+        s = GLVisualize.glscreen(
             "Plot",
             resolution = plt[:size],
             visible = visible
         )
-        @async GLWindow.waiting_renderloop(screen)
+        @async GLWindow.waiting_renderloop(s)
     end
     # now lets get ourselves a permanent Plotting screen
     plot_screens = get_plot_screen(GLVisualize.get_screens(), name)