flash_stats.py should use ConvexHull not raw triangulation

[deeplycloudy]

See warning in docs for Delaunay, which we currently use: https://github.com/scipy/scipy/blob/master/scipy/spatial/qhull.pyx#L1627

Instead:
https://github.com/scipy/scipy/blob/master/scipy/spatial/qhull.pyx#L2131