rref gives Left "Attempt to invert a non-invertible matrix"

Looks like `rref` gives wrong results:

```haskell
rref <$> (fromLists [[1, 2, 1], [(-2), (-3), 1], [3, 5, 0]] :: Maybe (Matrix 3 3 Double))
```

gives:

`Just (Left "Attempt to invert a non-invertible matrix")`

Although Python's sympy gives:

```python
m = Matrix([[1,2,1], [-2,-3,1], [3,5,0]])
m.rref()

(Matrix([
 [1, 0, -5],
 [0, 1,  3],
 [0, 0,  0]]), (0, 1))
```

