Weighted alternatives not working

I'm using v.3.20 and weighted alternatives don't seem to be working. 

I start an abtest with:
```
alternatives = {"alt1" => 9}, "alt2"
ab_test(:example, alternatives)
```

When I fetch the experiment with `Split::ExperimentCatalog.find('example')`, the `@weight` attribute of both Split::Alternative are equal to 1.