changed :size to :board size in order for it to make more sense as a parameter

When creating a new Game, board_size can be passed in, which is passed on to
Board.new in order to determine the size of the board
the board was outputting incorrectly because of an error in the loop size
fixed spec bug on #show caused by a bug in the #show method and changed specs that were using the old :size parameter to use the new :board_size
modified Board.new to take the :board_size parameter
modified game spec to accodmodate :board_size parameter