reference to GEMMI's orthogonalization matrix needs updating

[DHekstra]

in reindex.py,

105 | if force_rs or (not "rs_a" in ds.keys()):
106 | orthomat_list = ds.cell.orthogonalization_matrix.tolist()
107 | orthomat = np.asarray(orthomat_list)

gemmi now uses cell.orth.mat (see https://gemmi.readthedocs.io/en/latest/cell.html)

[minhuanli]

Hi Doeke, we’re aware that GEMMI’s API changed significantly in the 0.7.0 release and adapting to it will take some time. For now, please use gemmi==0.6.7.

[DHekstra]

that's what we're doing for now. thanks!