Minesweeper code improvement, noticed by Predrag

It wasn't actually removing the origin. The whole game
still worked as expected because of other checks but
removing the origin makes it more robust and faster
so it's a valuable improvement.

_posts/2024-07-16-minesweeper-100-lines-of-clean-ruby.markdown

@@ -138,7 +138,7 @@ Finally, if we hit a mine we exit early with `:lose`. Otherwise we check if all
 The only thing missing here is the neighbours method on the coordinate. We implement it by first creating a list of offsets to all 8 neighbours:
 ```ruby
 Coordinate = Data.define(:x, :y) do
-  NEIGHBOURS = (Enumerator.product([-1, 0, 1], [-1, 0, 1]).to_a - [0, 0]).map { |x, y| self.new(x, y) }
+  NEIGHBOURS = (Enumerator.product([-1, 0, 1], [-1, 0, 1]).to_a - [[0, 0]]).map { |x, y| self.new(x, y) }
   # ...
 end
 ```