fixed some minor formatting in stencil.py
fixed some minor formatting in stencil.py

pyamg/pyamg,kidaa/pyamg,huahbo/pyamg,pyamg/pyamg,pyamg/pyamg,huahbo/pyamg,huahbo/pyamg,kidaa/pyamg,kidaa/pyamg,kidaa/pyamg,huahbo/pyamg