Hist "quick example" is broken

```python
bins = np.linspace(0, 3, 61)
pdfs = np.random.random((100, 61))

ens_h = qp.Ensemble(qp.hist, data=dict(bins=bins, pdfs=pdfs))
```

I can fix it if i change number of `pdfs` to 60

Also `bins` and especially `pdfs` are not very self-descriptive names.