Make the cursor keys work in 5x5 again

The cursor keys stopped working in 5x5 once binding inheritance was
introduced in 0.6.0 (see Textualize#1343). Making them `universal` keys here fixes the
issue. This won't be the final form of this change, but this fixes this
example so that it works with 0.6.0 (so anyone cloning down the code and
running with an installed 0.6.0 will get the full effect).

Once the final work resulting from Textualize#1343 takes place this will need a final
update (and should be a good test example for the changes).

examples/five_by_five.py

@@ -166,10 +166,10 @@ class Game(Screen):
         Binding("n", "new_game", "New Game"),
         Binding("question_mark", "push_screen('help')", "Help", key_display="?"),
         Binding("q", "quit", "Quit"),
-        Binding("up,w,k", "navigate(-1,0)", "Move Up", False),
-        Binding("down,s,j", "navigate(1,0)", "Move Down", False),
-        Binding("left,a,h", "navigate(0,-1)", "Move Left", False),
-        Binding("right,d,l", "navigate(0,1)", "Move Right", False),
+        Binding("up,w,k", "navigate(-1,0)", "Move Up", False, universal=True),
+        Binding("down,s,j", "navigate(1,0)", "Move Down", False, universal=True),
+        Binding("left,a,h", "navigate(0,-1)", "Move Left", False, universal=True),
+        Binding("right,d,l", "navigate(0,1)", "Move Right", False, universal=True),
         Binding("space", "move", "Toggle", False),
     ]
     """The bindings for the main game grid."""