expert-othello.rb : Place GAME constant at top level.

I'm guessing this is broken because constant lookup changed somewhat between 1.8 and 1.9. With this change the game no longer errors out, but it doesn't seem to be working entirely correctly either. Although that might just be me not really understanding the game
Merge pull request #216 from arnebrasseur/othello

expert-othello.rb : Place GAME constant at top level.