Fix football doughnut labelling

By using bonzo's attr method

Fixes https://github.com/guardian/frontend/issues/5787 and https://github.com/guardian/frontend/issues/5785
Sorry, see what you mean. Safari 7 was actually borking when using `classList` (see https://github.com/guardian/frontend/issues/5785), was rendering

![screen shot 2014-09-01 at 16 47 42](https://cloud.githubusercontent.com/assets/74132/4110242/5c64597a-31ef-11e4-9394-8308fd4c19c8.png)