small fix for macosx build
small fix for macosx build

aaronzou/Shape-Deformation,JianpingCAI/libigl,JianpingCAI/libigl,JianpingCAI/libigl,JianpingCAI/libigl,aaronzou/Shape-Deformation,aaronzou/Shape-Deformation,JianpingCAI/libigl,JianpingCAI/libigl,aaronzou/Shape-Deformation,aaronzou/Shape-Deformation