Re-add 6.12.3 compatibility.
Re-add 6.12.3 compatibility.

lykahb/aeson,timmytofu/aeson,23Skidoo/aeson,nurpax/aeson,roelvandijk/aeson,jkarni/aeson,plaprade/aeson,sol/aeson,sol/aeson,abbradar/aeson,bwo/aeson,dmjio/aeson,aelve/json-x,neobrain/aeson,neobrain/aeson,sol/aeson,roelvandijk/aeson,beni55/aeson,JPMoresmau/aeson,SeanRBurton/aeson