They are practically the same thing, one says "you are not going nowhere" ("sehova nem"), the other says "you are not going nowhere, either" ("sehova sem"), the "either" referring to "nowhere". That is, you are not even going nowhere".
I think, grammatically, "sehova sem" is the "correct" version.

To illustrate the difference, consider these two sentences:
- I can't see anything
- I can't see a thing