Fix undying bullets bug

src/bullet.cr

@@ -4,11 +4,12 @@ class Bullet < Sprite
   include LxGame::SpriteAge
 
   def update(dt)
+    super
     update_position(dt)
   end
 
   def draw(renderer)
-    brightness = ((4.0 - @age) / 4.0) * 255
+    brightness = ((4.0 - self.age) / 4.0) * 255
     renderer.draw_color = SDL::Color[brightness, brightness, 0]
     renderer.draw_point(@position.x.to_i, @position.y.to_i)
   end

src/lx_game/sprite/age.cr

@@ -1,10 +1,9 @@
 module LxGame
   module SpriteAge
-    getter age : Float64 = 0.0
+    property age : Float64 = 0.0
 
     def update(dt : Float64)
-      super
-      @age += dt
+      self.age += dt
     end
   end
 end