add trailing underscore -> Indiv::fitness_

src/aevol_modify.cpp

src/libaevol/7/ExpManager_7.cpp

src/libaevol/7/Individual_7.cpp

src/libaevol/7/Individual_7.h

src/libaevol/7/Stats_7.cpp

...ost_treatments/aevol_post_ancestor_network_knockout_7.cpp

src/post_treatments/aevol_post_ancestor_stats_7.cpp