Bug for Ubuntu 17.10 and debian unstable, get_atom_positions

There seems to be a bug for Ubuntu 17.10 related to finding the atom positions.

The bug was discovered when the dummy data structure Fantasite was used, atom positions were not correctly found. There was no problems in 17.04. The analysis script that gives a good result in Ubuntu 17.04, but not in Ubuntu 17.10 and debian unstable is https://gitlab.com/atomap/atomap/blob/master/doc/images/003_make_fantasite.py.