lib/json{,_fwd}.hpp: upgrade to 3.9.1
Such an upgraded library is needed to compile on some non-standard systems.
Prochaines maintenances programmées: lundi 06/05, lundi 03/06, lundi 01/07
Pour plus d'informations: https://doc-si.inria.fr/display/SU/Gitlab
Such an upgraded library is needed to compile on some non-standard systems.