download-demo-data script does not work when zsync is installed

[Johannes Ring]

johannr@debian-t420s:dolfin (master)$ ./cmake/scripts/download-demo-data 
Downloading box_with_dent.xml.gz to demo/documented/eigenvalue
failed on url https://fenicsproject.org/pub/data/meshes/box_with_dent.xml.gz.zsync
could not read control file from URL https://fenicsproject.org/pub/data/meshes/box_with_dent.xml.gz.zsync
Downloading unitsquare_32_32.xml.gz to demo/documented/tensor-weighted-poisson
failed on url https://fenicsproject.org/pub/data/meshes/unitsquare_32_32.xml.gz.zsync
could not read control file from URL https://fenicsproject.org/pub/data/meshes/unitsquare_32_32.xml.gz.zsync
...

[Prof Garth Wells]

This would be resolved if we use git lfs . . .

[Prof Garth Wells]

Data is now stored using git lfs.