Smalltalk fix for Pharo tutorial section 28.2 at https://ci.inria.fr/pharo-contribution/job/UpdatedPharoByExample/lastSuccessfulBuild/artifact/book-result/FirstApplication/FirstApplication.html

Fix for 28.2 code

initialize
	| sampleCell width height n |
	super initialize.
	n := self cellsPerSide.
	sampleCell := LOCell new.
	width := sampleCell width.
	height := sampleCell height.
	self bounds: (5 @ 5 extent: (width * n) @ (height * n) + (2 * self borderWidth)).
	cells := Array2D new: 5 tabulate: [ :i :j | self newCellAt: i at: j].