stage2: Add apt-transport-https
stage2: Add apt-transport-https

Fixes RPi-Distro/repo#52

rkubes/pi-gen,timcoote/Pumpkin-gen,jannik-kramer/Mean,WLANThermo/pi-gen,BlokasLabs/modep,drothmaler/pi-gen,sam3d/pi-gen,timcoote/Pumpkin-gen,8devices/pi-gen,jacen92/pi-gen,barnacleos/build,cfstras/pi-gen,DigitaleGesellschaft/pi-gen,BenjaminEHowe/keyringpi-gen,RPi-Distro/pi-gen,timcoote/Pumpkin-gen,brindosch/pi-gen,KingBrewer/pi-gen,BlokasLabs/modep