Fixed types of variables in BMGame->get_json_data()

Fixes #143.

While testing this, I seem to have been getting an intermittent problem validating the QUnit tests through Firefox, but  not Safari.

test_Overview.getOverview (1, 3, 4)

TypeError: Api.completed_games is undefined
Source: 	

http://localhost:8080/ui/js/Api.js:255


I don't know if this is related at all to the changes that I made, or if it is independent of my changes.

Any ideas?