fix bug using -b flag in foldtest.py
fix bug using -b flag in foldtest.py

The -b flag made the bounds floats while the code requires integers for
the range suction

Caoimhinmg/PmagPy,lfairchild/PmagPy,lfairchild/PmagPy,Caoimhinmg/PmagPy,lfairchild/PmagPy,Caoimhinmg/PmagPy