Invert rulers insertion order.

Rulers insertion order impact the result of the bubble sort algorithm.
By inverting the order, we can make the output image looking more natural.

Awesome's screen properties can be seen like this:
* The screen has a geometry (its size) ;
* Inside there is the workarea ;
* Inside there is the tiling_area.

It seems better to draw rulers in this order.

tests/examples/screen/template.lua

@@ -293,14 +293,14 @@ end
 for _=1, screen.count() do
     local s = screen[1]
 
-    -- The outer geometry.
-    compute_ruler(s, s.geometry, "geometry")
+    -- The padding.
+    compute_ruler(s, s.tiling_area, "tiling_area")
 
     -- The workarea.
     compute_ruler(s, s.workarea, "workarea")
 
-    -- The padding.
-    compute_ruler(s, s.tiling_area, "tiling_area")
+    -- The outer geometry.
+    compute_ruler(s, s.geometry, "geometry")
 end
 
 -- Get the final size of the image.