Story: cells with less than two neighbours die

As a game producer
I want cells with less than two neighbours to die
So that I can illustrate how the game works to people with money

Scenario: cells with zero or one neighbour die

Given the grid looks like
........
.XX.XX..
.XX.....
....X...
........
When the next step occurs
Then the grid should look like
........
.XX.....
.XX.....
........
........