Add missing color argument in forward_canvas_draw_over_viewport example.

(cherry picked from commit 034c48dbeddbd88e88a2b3e45a2eb06ecf90bd81)

doc/classes/EditorPlugin.xml

@@ -199,7 +199,7 @@
 				[codeblock]
 				func forward_canvas_draw_over_viewport(overlay):
 				    # Draw a circle at cursor position.
-				    overlay.draw_circle(overlay.get_local_mouse_position(), 64)
+				    overlay.draw_circle(overlay.get_local_mouse_position(), 64, Color.white)
 
 				func forward_canvas_gui_input(event):
 				    if event is InputEventMouseMotion: