Fix for slow background updating

[ianni67]

Some notebooks may be very slow (my notebook is a bit old, for example), so it might be better to change the interval between two "samples" of the foreground mask. Otherwise the background/background border will be updated too slowly.
Unless Master Fiblan decides to add a controllable parameter to the application, in order to change such interval we have to modify the code a little bit:

cd fakecam
vi fake.py

go to row 91
change 30 to a more suitable value (for my veeery slow notebook, I changed it to 1).
close and run as per instructions.