Fix bug in computation of k in PhaseSchlick (Jean-Philippe Grimaldi)
Fix bug in computation of k in PhaseSchlick (Jean-Philippe Grimaldi)

patwonder/pbrt-v2-skin,patwonder/pbrt-v2-skin,patwonder/pbrt-v2-skin,patwonder/pbrt-v2-skin,patwonder/pbrt-v2-skin