Can this deal with complex numbers? 

Hi authors,

I intended to use this method on complex numbers and it turned out with a error message like:

`File "optimizer.py", line 701, in step
    step_size.div_(denom).clamp_(lower_bound, upper_bound).mul_(
RuntimeError: "clamp_scalar_cpu" not implemented for 'ComplexFloat'`

I'm wondering if it's possible to improve this for complex numbers? Thanks.

Ni