Should be able to change just one parameter of the three used to define a numpy function param

Ex.
```python
class P(Params):
    a = LinspaceParam(help='linspace', default=[0.0, 1.0, 100])

p = P()
p.get_numpy_fn_param('a')[1] += 5
print(p.get_numpy_fn_param('a'))  # prints [0.0, 6.0, 100]
```
