fix icon locations in demo projects

2d/fog_of_war/engine.cfg

@@ -2,7 +2,7 @@
 
 name="Fog of War"
 main_scene="res://fog.scn"
-icon="icon.png"
+icon="res://icon.png"
 
 [input]
 

2d/polygon_path_finder_demo/engine.cfg

@@ -2,4 +2,4 @@
 
 name="polygon_path_finder_demo"
 main_scene="res://new_scene_poly_with_holes.scn"
-icon="icon.png"
+icon="res://icon.png"

gui/input_mapping/engine.cfg

@@ -2,7 +2,6 @@
 
 name="Input Mapping GUI"
 main_scene="res://controls.scn"
-icon="icon.png"
 
 [display]
 

misc/tween/engine.cfg

@@ -2,7 +2,7 @@
 
 name="Tween Demo"
 main_scene="res://main.xml"
-icon="icon.png"
+icon="res://icon.png"
 target_fps=60
 
 [display]

misc/window_management/engine.cfg

@@ -2,7 +2,7 @@
 
 name="Window Management"
 main_scene="res://window_management.scn"
-icon="icon.png"
+icon="res://icon.png"
 
 [display]