example fix

[Matt--]

exposeNeighbours function was checking 4 rows & columns, not 3.

[DavePearce]

Ok, no this doesn't work ... the change is invalid, though I agree it is intuitive. Sadly, making it work would break other things, such as this:

function sum([int] xs) => int:
   int r = 0
   for i in 0 .. |xs|:
      r = r + xs[i]
   return r