Consider for instance,

```
In [2]: from sklearn.metrics import r2_score

In [3]: r2_score([0, 0], [2, 1])
Out[3]: 0.0

In [4]: r2_score([-1, 1], [2, 1])
Out[4]: -3.5
```
I expect `r2_score([[0, -1],[0, 1]], [[2, 2],[1, 1]], average=None)` to be equal to `np.array([0, -3.5])`.