yaml-to-latex.py assumes two reviewers

[weinman]

It's easy enough to edit locally, but these lines in yaml-to-latex.py cause problems when there is not a second reviewer (as in the case for the ten year reproducibility challenge).

It also seems the template assumes this too, which is a problem with these lines.

[rougier]

It's kind of a recurrent problem, especially for the ten years challenge where only one reviewer is needed. If you leave the second reviewer empty (not even a space), it is supposed to work but it's kind of very fragile. A PR would be most welcome.