Update Grids.m
Update Grids.m

fixes a few typos.

Signed-off-by: ghurstunither <1e321e53ca8d7b31cb9b5a4008934e2cf6ee2e18@users.noreply.github.com>

dreamworksanimation/openvdb,dreamworksanimation/openvdb,dreamworksanimation/openvdb,dreamworksanimation/openvdb