Fix creating virtual environment for stub creation

[tekktrik]

Fixes a small bug I noticed

[tekktrik]

I did not realize a space was not needed!

[jepler]

If the latter form is more standard and creates less confusion, we should change it

[tekktrik]

Okay, I just reopened it then. I do typically see -m venv-name as opposed to -mvenv-name, and our own library instructions use that first form.

[jepler]

Thanks! it works either way, but "-m venv" is more standard and clearer.