stc.experimental.ndslice -> sci.ndslice

[Ilya Yaroshenko via Digitalmars-d]

We plan to add a set of numeric packages and this would be real 
pain if they would be one-by-one moved from experimental to 
stable std. So sci.* should be considered as experimental during 
few years.

https://github.com/dlang/phobos/pull/4207