option yLabel is ignored

as a proof I submit this code snippet:

```js
var nsamples = 1000;
var model = function() {
  var A = flip();
  var B = flip();
  var C = [A, B];
  return C;}
var product = Infer({method: 'enumerate', model: 'model'}, model)
viz.hist(product, {xLabel: '(A, B)', yLabel: 'P(A, B)'})
viz.hist(repeat(nsamples,model), {xLabel: '(A, B)', yLabel: 'P(A, B)'})
```